MILKFISH, Chanos chanos (FORSSKAL, 1775), FRY SEASONALITY IN VANUATU: THEIR AVAILABILITY AND ABUNDANCE IN THE COASTAL SHORELINE OF EFATE ISLAND

By

Ronnick Spenly Shedrack

A Thesis submitted in fulfillment of the requirements for the Degree of Master of Science in Marine Science

Copyright © 2017 by Ronick Spenly Shedrack

School of Marine Studies

Faculty of Science, Technology and Environment

The University of the South Pacific

November, 2017

Statement by Autho

I, Ronick Spenly She

best of my knowledge

overlapping with mat

institution, except wh

Signature:

Name: Ronick Spenl

Statement by Superv

The research in this th

knowledge is the sole

Signature:

Name: Dr. Marta Fe

Declaration of Originality

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drack, declare that this thesis is my own work

e, it contains no material previously publishe

terial submitted for the award of any other de

here due acknowledgement is made in the text

Date: 10 November

ly Shedrack Student ID No: S110

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hesis was performed under my supervision an

e work of Mr. Ronick Spenly Shedrack.

Date: 20/11/2

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Dedication

This thesis is dedicated to my dear parents Belinda Toa Spenly and Spenly Shedrack

Salemomo.

iv

Acknowledgements

I express my sincere thanks and appreciation to the Australian Centre of Agricultural

Research (ACIAR) for funding me for the Master of Science degree under the

ACIAR-USP scholarship Scheme and to USP for facilitating the sponsorship and

funding another 6-month for the write up until completion of the program.

The completion of my thesis was made possible through the invaluable support from

my principal supervisor, Dr. Marta Ferreira and co-supervisor, Dr. Susanna Piovano

who provided constructive criticism, suggestion, comments and encouragement

during the course of the study.

Dr. Marta is also immeasurably valued for providing me with support to Otolith

analysis technique that is necessary to complete the thesis. I also acknowledge Dr.

Susanna for various constructive criticisms polishing this study.

I express my appreciation to Mr. Sompert Gereva for his invaluable support, advice

and assistance throughout the project with the field data collection, sampling

materials and providing me space at the Vanuatu fisheries department to complete

the thesis write up. Thanks are also extended to Dr. Timonthy Pickering for his

various advices on the field data collection techniques.

I also express my gratitude to the Vanuatu Meteorological and Geo-hazard

Department staff particular, a special thanks to Melinda Natapei, David Gibson and

Philip Mansale for supporting with the data collection until the completion of the

fieldwork.

I would like to thank Martinez and his colleagues (2006) for allowing me to

reproduce their figure of milkfish life stages in Figure 1.2.

My heartfelt gratitude is extended to my family members, in particular Christian

Shedrack, Semion Shedrack, Ajay Shedrack, Susila Salemomo and Welpi Tane for

assisting me throughout the field data collection.

Lastly, I am thankful to my then girlfriend and now my wife, Rose Charley for her love, support and assistance with lab work, food preparation and for everything, she did for me.

v

Abstract

This study describes the seasonality and abundance of milkfish Chanos chanos fry in

the coastal shorelines of Efate Island in order to assess the feasibility of milkfish

aquaculture in Vanuatu. The study will enable the knowledge of fry collection so that

this species can be cultured for food. Four sampling sites have been assessed in

February 2016 for the presence of milkfish fry namely, Erakor, Kawenu, Mele and

Teouma. The site with the highest abundance was selected for further seasonality

sampling over a one-year period from February 2016 to February 2017.

Milkfish fry were collected from February to May and October to December 2016

and, again from January to February 2017. Milkfish fry was absent in other months

of the year. Two peaks of fry occurrence were observed, the 1st peak was in April and

the 2nd peak was in November. The fry abundance in Teouma was high (relative to

other locations such as Erakor, Kawenu and Mele) over the period of seasonality

sampling. The abundance between Moon phases showed that more fry were caught

in New Moon and 3rd quarter Moon whereby a non-significant difference (p > 0.05)

was observed. Milkfish fry collected on Teouma coast measured between 8 mm to 15

mm total length (TL) and the weight range was between 3 mg to 9 mg. The fry were

aged 13 to 25 days old, which mean that they spend 2 to 4 weeks in the surf zone

before disappearing into other habitats. Environmental variables assessed showed

cloud cover is positively correlated with fry abundance, similarly, wind speed and

current speed with length, and rainfall and turbidity with weight. Other variable such

as temperature in situ do not significantly correlated with fry abundance, weight and

length.

The prolonged fry seasonality in Vanuatu is advantageous for milkfish fry

aquaculture, however the very low abundance documented in Teouma are not.

Before a final decision on the viability of milkfish culture in Vanuatu is made, an

assessment of multiple sites is recommended. To be cost-effective such a study could

be informed by this research with sampling limited to the months when fry

abundances peaks. If milkfish culture does proof to be viable, then the landowners of

fry collection ground may need to manage activities along the coast to reduce

impacts on fry recruitment habitat. Furthermore, fishers may want to consider

vi

managing fishing of milkfish during spawning periods in order to protect spawning

stocks.

vii

Abbreviation and Acronyms

ACIAR Australian Center for International Agricultural research

ANOVA Analysis of variance

BOD Biological demand for oxygen

CT Concentration test oC Degree Celsius

DO Dissolve oxygen

FAO Food and Agricultural Organization

GSI Gonadosomatic Index

IPCC Intergovernmental Panel on Climate Change

VFD Vanuatu Fisheries Department

PIC Pacific Island Country

ppt Parts per thousand

VMGD Vanuatu Meteorology and Geo-hazard Department

COSPPac Climate and Ocean Support Program in the Pacific

SST Sea surface temperature

SPC Pacific Community

USP The University of the South Pacific

TL Total length

viii

Table of Contents Acknowledgements ..................................................................................................... iv

Abstract ........................................................................................................................ v

Abbreviation and Acronyms ...................................................................................... vii

List of figures ............................................................................................................... x

List of tables ............................................................................................................... xii

Thesis organisation.................................................................................................... xiii

Introduction .................................................................................................................. 1

1.1 Milkfish aquaculture ...................................................................................... 1

1.2 Reviews on milkfish (Chanos chanos) .......................................................... 1

1.2.1 Systematics .................................................................................................. 2

1.2.2 Morphology ................................................................................................. 3

1.3 Habitat and life history .................................................................................. 3

1.3.1 Life history ................................................................................................... 4

1.4 Food, Growth and Feeding Habit .................................................................. 7

1.5 Milkfish distribution ...................................................................................... 7

1.6. Milkfish aging, spawning and fry seasonality ................................................... 8

1.6.1 Milkfish spawning ....................................................................................... 9

1.6.2 Seasonality of fry ....................................................................................... 10

1.7 Migration and movement of fry ....................................................................... 11

1.8 Predation on milkfish fry .................................................................................. 12

1.9 Overview of main methods of fry collection .................................................... 12

1.10 Food demand in the Pacific island countries .................................................. 14

1.11 Conclusion ...................................................................................................... 16

1.12 Research objectives ........................................................................................ 16

Chapter 2: Methodology ............................................................................................ 18

2.0 Site selection and description ........................................................................... 18

2.1 Sampling materials and methods ...................................................................... 20

2.1.1 Sampling materials .................................................................................... 20

2.1.2 Bulldozer net construction ......................................................................... 21

2.1.3 Sampling method ....................................................................................... 23

2.2 Fry identification .............................................................................................. 24

2.3 Fry length and weight measurement ................................................................ 24

ix

2.4 Otolith analysis ................................................................................................. 25

2.5 Data analysis ..................................................................................................... 26

Chapter 3: Results ...................................................................................................... 27

3.1 Site assessment and selection ........................................................................... 27

3.2 Milkfish fry occurrence in Teouma .................................................................. 29

3.2.1 Monthly occurrence and abundance .......................................................... 29

3.2.2 Milkfish fry length and weight .................................................................. 30

3.3 Effect of Moon phases ...................................................................................... 32

3.3.1 Abundance by Moon phase........................................................................ 32

3.3.2 Total length and weight in Moon phase over one year .............................. 33

3.4 Comparison of fry abundance with other indices ............................................. 34

3.4.1 Environmental variables correlation with fry abundance .......................... 34

3.4.2 Environmental variables correlation with length and weight of milkfish fry ............................................................................................................................ 35

3.5 Otolith analysis and age of the fry per month and spawning estimates ........... 37

3.6 The age distribution .......................................................................................... 38

3.7 Spawning time estimates for Teouma over one year period ............................ 40

3.8 Comparison of fry abundance in the Melanesian PICs .................................... 41

Chapter 4: Discussion ................................................................................................ 42

Chapter 5: Conclusion ................................................................................................ 50

References .................................................................................................................. 52

Appendix .................................................................................................................... 66

Appendix A. Table of p-values for the ANOVA test ............................................ 66

Appendix B. The daily SST from VMDG and monthly mean, maximum, minimum, median and standard deviation beginning from February 17th 2016 to February 17, 2017. ............................................................................................. 69

Appendix C. Milkfish fry mean length and weight plus the descriptive statistic for Teouma over one year period ....................................................................... 70

x

List of figures

Figure 1.1 Picture of adult milkfish……………………………………………...…...2

Figure 1.2 Milkfish life cycles, 1-7 indicates the seven development stages in the

milkfish life cycle (obtained with permission from Martinez, Tseng et al. (2006)…..4

Figure 1.3 A graphical representation of peak and lean season of milkfish fry occurrence in several countries with data retrieved from Kuo et al. (1979),Villaluz (1986) and Vuto et al. (2014)…..………………………………………...………….19

Figure 2.1 Map of Vanuatu where the study is based. Retrieved from

http://www.nationsonline.org/oneworld/map/vanuatu-map .…….…………….……...19

Figure 2.2 Map of the four sites Erakor, Kawenu, Mele and Teouma where milkfish

fry was assessed during the preliminary study, and the Vanuatu capital (marked with

a star)…………………………………..………………………………………….…20

Figure 2.3 The bulldozer net built and used for this study. Picture shot at Teouma on

March 2016. ……………..……………………………………….…………………22

Figure 2.4 The bamboo frame design for the bulldozer net (Pickering, Tanaka et al.

2012)…………………………………………………….………………………..…22

Figure 2.5 Net size and design modified from Pickering, Tanaka et al. (2012)..…...23

Figure 2.6 Milkfish fry collected in a white plastic basin for visual identification. The

black dot from left to right showed position of grey spot on caudal fin, dark spot on

middle of body (air bladder) and two dark spot (eyes) on side each side of head…..24

Figure 3.1 Milkfish fry total abundance (number of fry captured during the

exploratory trial done on Teouma, Erakor, Mele and Kawenu). The different letters

indicate significant difference in abundance (p < 0.05) while the same letter indicate

no significant difference (p > 0.05).…………………………………………….…...29

Figure 3.2 Milkfish fry abundance and occurrence with SST by month for Teouma.

The different letters indicate significant difference in fry abundance (p < 0.05)..….30

Figure 3.3 The total length frequency of milkfish fry (N = 369) in the Teouma……31

xi

Figure 3.4 The frequency distribution of milkfish fry (N = 369) weight in

Teouma……………………………………………………………………………...31

Figure 3.5 Milkfish fry mean total length (A) and weight (B) by month of

occurrence. The error bars represent the standard deviation of the mean. …….…...32

Figure 3.6 Milkfish fry cumulative abundance in all Moon phases for Teouma

throughout the year. The different letters indicate significant difference is abundance

between Moon phases (p < 0.05). ……………………………….........…………….33

Figure 3.7 Milkfish fry mean total length (A) and weight (B) in four Moon phases.

The different letters show significant difference in mean total length or weight (p <

0.05) and the error bars represent the standard deviation of the mean. .……..……..34

Figure 3.8 The environmental variable correlation with milkfish fry abundance,

rainfall, cloud cover, wind speed, temperature, turbidity (transparency) and current

speed...……………………………………………………………………………....35

Figure 3.9 Environmental variable, temperature, cloud cover, rainfall, turbidity

(transparency), wind speed and current speed correlation with milkfish fry total

length ..…………………………………………………………..…………………..36

Figure 3.10 Environmental variables, temperature, cloud cover, rainfall, turbidity

(transparency), wind speed and current speed, correlation to milkfish fry weight

...…………………………………………………………………………..…………37

Figure 3.11 Photographs a, sagittae otolith from 14 days old larvae, 11 mm total

length (TL). (x400), b an otolith of a 15 day larva of 11 mm TL and, c a otolith of a

22 day larva of 14 mm TL. In photograph a, letters. A, anterior; P, posterior; D,

dorsal; V, ventral. The dot (●) are the increment dark zone, the star ( ) indicate the

core and the arrow (↓) indicate the discontinuity zone. …………...………………..38

Figure 3. 12 The age frequency of milkfish fry in Teouma coastal shoreline ….…..39

Figure 3.13 The mean age of fry per month of occurrence in Teouma. The error bars

represent the standard deviation of the mean. ..………...…...………………………39

Figure 3.14 Correlation between the age and length of milkfish fry ………….……40

xii

Figure 3.15 The spawning season of milkfish fry (N =63) based on different days over a one year period with mean Monthly SST…………………...……………….41

List of tables

Table 3.1 The monthly environmental parameters (turbidity (transparency), current

speed, salinity and SST) assessed and the landscape features for Mele, Kawenu,

Erakor and Teouma. The monthly values are presented as mean ± standard

deviation…………………………………………………………………………..…28

Table 3.2 the fry abundance between Fiji, Solomon Islands and Vanuatu……….....41

xiii

Thesis organisation

There are six chapters in this thesis.

Chapter 1 presents a literature review about what is known and where the gaps of

knowledge which require further research on milkfish (Chanos chanos) larval

recruitment. Other parameters affecting milkfish larval development and fry

presence along coastal areas were also reviewed, and seasonality of spawning

and culture of milkfish in the Pacific Island Countries (PICs) were outlined. This

chapter also presents the purpose and scope of the study, and the hypotheses and

statement of problems to be addressed. The reason for a milkfish fry seasonality

study in Vanuatu is also outlined and the advantages of having an additional fish

species for the local aquaculture industry are discussed.

Chapter 2 describes the materials and methods used to undertake this study. The study

sites and the methodologies applied to collect the larvae are shown and the data

and statistical analyses highlighted.

Chapter 3 presents the results that include seasonality of fry occurrence and abundance,

abundance in Moon phases, environmental variables affecting abundance and

size of fry, and finally the spawning period estimation.

Chapter 4 contains the discussion of research findings and reflection within the literature

context. The assessment for each single site was discussed with respect to the

abundance of milkfish fry and the parameters assessed. The length, weight and

age frequency of milkfish fry were also discussed with respect to seasonality and

Moon phases.

Finally, chapter 5 contains the conclusion and recommendations for further research to

address limitations and constraints in this study and to further engage researchers

to develop milkfish farming in Vanuatu.

1

Introduction

1.1 Milkfish aquaculture

Milkfish Chanos chanos is one of the many species cultivated to address food

shortage and meet the food protein demand in the Asian-Pacific region (Agbayani et

al. 1989; FAO 2014; Martinez et al. 2006). The knowledge about biology, spawning

and culture of the species has aided the development of milkfish culture industry in

many countries, in particular Asian nations (Bagarinao 1991; Martinez et al. 2006;

Sulu et al. 2016). Milkfish aquaculture dated back about 4 to 6 centuries ago in India,

Philippines, Indonesia and Taiwan (Agbayani et al. 1989; Nelson 2007). The prolong

season of fry appearance aids aquaculture development as fry can be collected and

stocked in water ponds in many months of the year (Bagarinao et al. 1987). In recent

decades, many Asian countries have used technological advances to move into

milkfish mass aquaculture. Pacific Island Countries and Territories (PICTs), milkfish

aquaculture is new, while in Nauru milkfish culture is part of their tradition for

household food consumption (Spennemann 2002). Vanuatu is one PIC with no

quantitative records of milkfish fry appearances or history and culture, however

there is history of local people collecting juveniles on some islands for food

(Pickering et al. 2012).

The knowledge of milkfish fry seasonality is lacking in some PICs although milkfish

fry are available in their coastal areas (Dela Cruz 1997). This knowledge is important

for PICs to adopt milkfish culture, as access to advanced hatchery technology is poor

and culture may depend on availability of wild fry for stocking ponds. Hence, the

purpose of this study is to determine milkfish fry seasonality in Vanuatu and evaluate

the potential of milkfish aquaculture.

1.2 Reviews on milkfish (Chanos chanos)

Milkfish Chanos chanos (Forsskål, 1775) is the only fish species of the family

Chanidae in the order Gonorynchiformes that comprises four families, seven genera

and 27 species (Bagarinao 1994b; Lim et al. 2002; Nelson 2006). The specific

2

epithet chanos (Greek for a fish of remarkable voracity) was attributed to milkfish in

1775 by the Swedish naturalist Peter Forsskål, who made a clear description of the

fish based on a specimen from the Red Sea that was preserved at the Zoological

Museum of the Copenhagen, University in Denmark (Klausewitz 1965). In 1803, the

French naturalist Bernard Germain de Lacépède elevated the specific epithet to the

generic level, naming the species Chanos arabicus, and further works from other

authors later described the milkfish under different names and synonyms (Bagarinao

1994b; Bagarinao 1991; Brian 2015). The review by Bagarinao (1994b) revealed that

nine different names were used to describe milkfish by Cuvier and Valenciennes

while other authors described it under eighteen other synonyms. The name Chanos

chanos was validated and used first by Klunzinger (1870) and following authors did

the same (Fricke 2008) .

A picture of a typical adult milkfish is shown in figure 1.1 whereby it has a single

dorsal fin, large fork tail and silver or milk colour. The milkfish swim over the sandy

bottom and around islands where coral reefs are present (Figure 1.1).

Study species: Chanos chanos

Kingdom: Chordata

Phylum: Vertebrata

Class: Osteichthyes

Order: Gonorynchiformes

Family: Chanidae

Genus: Chanos (Lacépède, 1803)

Species: Chanos chanos (Forsskål, 1775)

Figure 1.1 Picture of adult milkfish (Source: www.aqtinfo.com)

1.2.1 Systematics

Milkfish is considered a more ancestral ostariophysian which belongs to a Monotype

gonorynchiform family and is related mostly to the freshwater Ostariophysi

(Bagarinao 1994b). Although milkfish morphological characteristics have

significantly contributed to a much better understanding of the species, molecular

3

studies determined the number of chromosomes in milkfish as diploids, 2n = 32

consisting of 7 pairs of metacentric, 2 pair of submetacentric and 7 pair of

acrocentric pairs of chromosomes (Arai et al. 1976). The number of chromosomes is

low when compared to other primitive teleosts (Brian 2015). The genetic

identification has helped to distinguish milkfish populations, whereby 9 populations

were described in the Indo-Pacific of which 4 populations were determined as the

Indian, Thailand, Philippine-Taiwan-Indonesia and Tahiti (Bagarinao 1994b;

Bagarinao 1991; Kumagai 1990; Senta et al. 1977). Samples of larvae and juvenile

specimens obtained from Kiribati, Tonga, Hawaii and Panama have revealed four

other populations and a suggestion was made that there is a possibility for one

population in the coast of Africa (Bagarinao 1994b).

1.2.2 Morphology

Adult milkfish has been described as having a silvery colour, muscular, streamlined

body and powerful forked tail (Bagarinao 1994b). Recently Brian (2015) stated that,

“The mouth is small and lacks teeth. There is a notch on the upper jaw in the mid-

line into which a lower jaw protuberance fits. The large eyes have an adipose eyelid.

The intestine is very long with many folds. The lower part of the esophagus has a

"gizzard”, an area with longitudinal folds. Lateral line scales 70-92, with 3-11 on

the tail fin”.

There are also variant forms of milkfish reported, the “goldfish” form from

Philippine and Indonesia and the “dwarf or hunchback –shade type” found in

Hawaii, Indonesia and Australia, but the knowledge about these other forms of

milkfish is limited since they rarely occur (Bagarinao 1994b).

1.3 Habitat and life history

Milkfish are usually found in offshore marine waters and shallow coastal

embayment, but also frequently enter estuaries and occasionally penetrate freshwater

streams (Bagarinao 1994b). Adults occur in small to large schools near the coasts or

around the islands w

and larvae are pelagic

in coastal wetlands

(Bagarinao et al. 198

sexually and spawn i

phytoplankton and z

benthic invertebrates

Milkfish at the differ

the open ocean in adu

spawn (Figure 1.2).

Figure 1.2 Milkfish limilkfish life cycle (ob

Milkfish fry enters a

juvenile habitat. Acco

in estuaries and near

of water flow (Lin et

swamps and lagoons

1.3.1 Life history

The life history and

many researchers, a

4

where reefs are well developed (Bagarinao 19

c for up to 2-3 weeks and older larvae migrat

(mangroves, estuaries) occasionally enterin

87). Juveniles and sub-adults return to the sea

in fully saline marine water (Nelson 2007). M

zooplankton; juveniles and adults feed on cy

s, and even pelagic fish eggs and larvae

rent life stages frequent various habitats befor

ult stage where they spend the rest of their li

ife cycles, 1-7 indicates the seven developmenbtained with permission from Martinez, Tseng

a coastal lagoon and swamp before they m

ording to Martinez et al. (2006), milkfish fry

river mouth. The fry tend to migrate into riv

t al. 2003; Pillay et al. 2005) and other coas

to enter into juvenile stage.

habitat of milkfish in the wild was docume

although many errors have been pointed o

991). Milkfish eggs

te inshore and settle

ng freshwater lakes

a where they mature

Milkfish fry feed on

yanobacteria, small

(Bagarinao 1991).

re they migrate into

ves and continue to

nt stages in the g et al. (2006)

migrate further into

y are more abundant

vers in the direction

stal habitats such as

ented in the past by

out in more recent

5

research, like the review by Bagarinao (1994b). In the last few decades milkfish have

been demonstrated to mature and spawn under various condition of captivity, and

hatcheries have produced larvae to supply ponds (Bagarinao 1991). Nowadays the

aquaculture industry has employed facilities and techniques that facilitate breeding in

captivity and the transition of fry to juvenile in captivity, including mass propagation

with minimum mortality (Bagarinao 1991; Nelson 2007).

Milkfish fertilized eggs are spherical and pelagic with a diameter ranging from 1.1 to

1.2 mm, and the development of the embryo takes 20 - 35 hours at a temperature

range from 26 ºC to 32 ºC, and at a salinity between 29 to 34 parts per thousand (ppt)

(Bagarinao 1991). Delsman (1926) was the first scientist who took note of milkfish

eggs when he examined the oocytes and later collected 15 eggs from the Java sea;

later his identification was tested and proven to be correct after induced spawning

was done in captivity (Bagarinao 1994b; Liao et al. 1979) . The spawning grounds of

milkfish are in clean and clear saline water with warm temperature (25-30 ºC) and

shallow water (< 200 m) over coral reefs and sandy beaches at a distance of about 6

km offshore (Brian 2015). The spawning location is also based on the need to

minimize predation (Brian 2015), and close to shore to enhance larvae migration to

coastal habitat (Johannes 1978).

Milkfish larvae are categorized into 5 developing stages: i) yolk-sac larvae (3.3-5.4

mm total length (TL), lasts for 3 days); ii) pre-flexion larvae (3.4-6.2 mm TL, lasts

for 5 days); iii) flexion larvae (4.4-9.9 mm TL, lasts for 6 days); iv) post flexion

larvae (9.5-14.9 mm TL, lasts for 7 days); and v) transformation larvae (9.5 -16.5

mm TL also named as fry are free swimming larvae, last from 2 to 4 weeks), after a

detailed description was made by various authors (Bagarinao 1991). Milkfish larvae

are pelagic, while at hatching, the yolk sac larvae are about 3.5 mm TL; the lava

begin to feed when their eyes are fully pigmented (3 days old) and the mouth will

open although some yolk is still attached (Bagarinao 1994a). It takes 36 hours for the

larvae to grow into 5 mm total length and to consume about 90 % of the yolk until

day 5 when the yolk is completely exhausted. The size of the egg, larvae, amount of

yolk and mouth is far greater in milkfish than any other tropical marine fish

(Bagarinao et al. 1986). Younger larvae occur both onshore and offshore while older

larvae are found near shore only (Bagarinao et al. 1987). A study on larvae

6

movement in the Great Barrier Reef by Leis et al. (1991) revealed that the larvae

move to the juvenile habitat through passive advection and active migration. Active

migration is employed by larvae that gain a certain degree of morphological

characteristics, probably at 10 mm TL and age of 2 weeks old (Bagarinao 1994b).

The juvenile milkfish has a minimum length of 20 mm and the shape and structures

of adult (Bagarinao 1994b; Bagarinao 1991). The juveniles, length between 2 to 10

cm TL, are called “fingerlings”, particularly in the aquaculture industry (Bagarinao

1994b). Milkfish larger than 30 cm are found in a variety of habitats such as

estuaries, coral lagoons, tidal creeks, mud flats and tide pools that are protected areas

and characterized by rich food supply (Buri 1980; Kumagai et al. 1985; Kumagai et

al. 1981). The juveniles feed mainly on food from the bottom such as cyanobacteria,

diatoms, detritus, filamentous green algae and invertebrate such as worms and

crustacean (Bagarinao 1994b; Bagarinao 1991). The wild juveniles feed during the

day as determined by gut content analysis, whereby morning guts were empty while

those during the day were loaded with food (Kumagai et al. 1985).

An adult milkfish has a length of 50-150 cm TL and weight range of 4-14 kg with

age from 3-15 years (Bagarinao 1991). More recently, Brian (2015) has noted in a

review of the milkfish of Iran that this species has the size of up to 1.85 m and 18.6

kg. Adult milkfish are powerful swimmers and are seen in large schools near islands

and the coast where reefs are well developed, and also in coastal lagoons where they

often swim with their dorsal fins above water like sharks (Bagarinao 1994a; Brian

2015). Adults are seen and caught near shore usually during breeding season

(Kumagai 1990; Tampi 1957). Milkfish reproduction in the wild is not well

understood, although milkfish has been successfully bred in captivity in the

Philippines, Taiwan, Hawaii and in Indonesia, and in Kiribati (Bagarinao 1994b). In

nature milkfish may reach sexual maturity at age 3-5 years and in captivity at age 8-

10 years (Bagarinao 1994b; Brian 2015). The females may spawn more than twice

per year, both in captivity and in the wild (Marte et al. 1986b; Schuster 1960; Silas et

al. 1982; Tampi 1957), and 3-13 kg female may produce 0.5 to 6 million eggs.

Spawning usually happens at night and is triggered by lunar and seasonal periodicity

(Kumagai 1990; Marte et al. 1986b).

7

1.4 Food, Growth and Feeding Habit

Milkfish larvae normally feed on phytoplankton and zooplankton (Bagarinao 1991;

Brian 2015), and juveniles in a variety of food, including cyanobacteria, detritus,

diatoms, filamentous green algae, fish eggs and larvae, and some invertebrates such

as crustaceans and worms (Bagarinao et al. 1986). Milkfish larvae are particulate

visual feeders. They feed by snapping prey such as rotifer, water flea, copepod and

brine shrimp (Bagarinao 1991). However, Carreon et al. (1984), evaluated the

feeding response of larvae on diets of plankton and detritus (containing bacteria,

various species of cyanobacteria, diatoms, rotifers and protozoans) in race way tanks

whereby growth, health and survival was better in larvae supplied with natural

planktons in comparison to those reared on detritus.

An adult milkfish feeds on plankton, benthic plants and animals (Bagarinao 1994b),

they feed on plankton by swimming through plankton masses and also larval fish

schools. They also graze on the rock's surface and floating algae therefore, adult

milkfish is an opportunistic generalist (Bagarinao 1994b). Although juveniles and

adult milkfish feeds on both day and night they are more active during the day

(Kawamura et al. 1981).

1.5 Milkfish distribution

Milkfish are widely distributed in tropical, subtropical seas and around Oceanic

islands, where seawater temperatures are greater than 20 °C, ranging from Red Sea

and African coast to East Pacific, South Pacific coast of the U.S.A, Central America,

Central and Western Pacific, Northern Pacific, South Pacific to New Zealand, the

Indian Ocean and around Australia (Figure 1.3). Milkfish is said to be an Indo-West

Pacific fish species, although it ranges across, to the eastern Pacific (Brian 2015).

The adults can swim at the speed of 2 km/h although they were never caught in the

high seas (Brian 2015). It is thought that milkfish recolonized the eastern Pacific by

dispersal from the Indo-West-Pacific via the equatorial counter current (Briggs

1961), even though there is still debate regarding these theory (Bagarinao 1994a;

8

Bagarinao 1991; Brian 2015; Leis 1984). Milkfish are not found in tropical waters

that are affected by cold ocean currents (Bagarinao 1991).

1.6. Milkfish aging, spawning and fry seasonality

Otoliths are fish ear bones, small calcified structures found inside the inner ear

region to help with hearing and orientation (Begg et al. 2005; Popper et al. 2005).

The shapes are different for each three type of otolith such as the lapilli, sagittae and

asterisci (Panfili et al. 2002). The sound wave is detected from the movement of

otolith and the fish movement that send mechanical signals which assist in hearing

and orientation (Popper et al. 2005).

Otoliths have been used widely to determine age, growth rate, development and life

history of fish and are helpful in understanding fish systematics and evolution (Fey et

al. 2005; Popper et al. 2005). Otoliths are formed at the hatching of the eggs and

grow daily rings made of calcium ion from the endolymph precipitate (Warner et al.

2005). The rings continue to grow around the core and form a layer called

microstructures, increment or growth rings. The daily growth rings or increments

become narrower as the fish age increase, which also pose a difficulty in determining

the life history of older fish (Baumann et al. 2005).

The growth of milkfish larvae follows a sigmoid growth curve (Liao et al. 1979).

Kumagai et al. (1981) stated that fry in shore waters grow at a rate of 0.5 mm per

day. Tzeng et al. (1988) have determined that the first otolith increment in reared

milkfish larvae is formed 2 days from hatching and continues on a daily basis. A

subsequent study by Tzeng et al. (1989) on wild caught larvae using the

oxytetracycline method has validated that increments form at the rate of 1 per day

regardless of growth rate. Kumagai (1990) has determine the size distribution

frequency of 10,000 milkfish fry collected in shore waters where he concluded that

shore caught fry grow at the rate of 0.5 mm/day and larvae remains at 5 mm for

about 4 days from hatching. Therefore the relationship between size and age was

derived from the following equation (Equation 1) from Bagarinao (1991).

Equation 1: TL = 5.0 + 0.5 (D-4)

9

Where, TL=total length and D=day from hatching

Furthermore, the growth of shore caught milkfish fry is temperature dependent and

the transformation stage begins in 5 days of rearing (Villaluz et al. 1983a). The

growth of fry also varies with factors such as diet and feeding (Bagarinao 1991).

1.6.1 Milkfish spawning

The spawning age of milkfish was determined to be 3 to 10 years in a temperature

range of 25 to 30 °C and salinity of 29 to 34 ppt (Bagarinao 1991). Milkfish females

can produce large amount of eggs with ovaries weighing 10 % to 25 % of the body

weight when mature (Bagarinao 1991). The frequency of spawning as mentioned

previously occurs probably more than once per year, based on indications from a

female caught in the Philippines that contained 3-4 batches of oocytes with different

sizes (Bagarinao 1991).

In captivity, female milkfish at the Southeast Asian Fisheries Development

Centre/Aquaculture Department (SEAFDEC/AQD) can spawn to a maximum of

three times per year naturally (Marte et al. 1986a). Spawning occurs around midnight

and this was confirmed based on the egg development stages that were collected in

the Panay island in the Philippines (Bagarinao 1991), although spawning at day time

can occur less frequently. Spawning behavior of milkfish was observed in floating

cages at the SEAFDEC/AQD in Philippines whereby an increase in swimming

activity, chasing, leaping and slapping of water is seen from afternoon to early

evening.

Milkfish spawning was assessed in the Philippines in Moon phases whereby the

spawning occurred around midnight of every 1st and 3rd quarter Moon phase

(Bagarinao 1991). It was also suggested by Delsman in 1929 that, spawning during

neap tide minimize flushing of the eggs and facilitate larvae to remain in near shore

waters (Bagarinao 1991), and the same was also suggested by Johannes (1978) for

marine species in the tropical region with pelagic eggs. The young milkfish larvae

are more abundant in quarter Moon phases and older ones on the New and Full

Moon phases while fry were more abundant during New Moon and Full Moon of

10

which the same occurrence happened in the Philippines and other localities

(Bagarinao 1991; Kumagai 1984).

1.6.2 Seasonality of fry

Many authors have determined seasonality and the occurrence of milkfish fry in

different countries. Villaluz (1986) stated that milkfish fry seasonal occurrence may

be predictable but the abundance will vary from year to year. The season is long near

the equator and becomes shorter at the higher latitudes and in regions affected by

trade winds or monsoon. The peak season may coincide with one or both of the

yearly wind shifts (Villaluz 1986).The seasonality of milkfish fry has been

determined for Fiji with a seasonal peak from December to February (Villaluz 1990)

and for Kiribati with two (2) seasonal peaks, one from late December to early

February and the other from May to September (Wainwright 1982). The

identification of peak seasons is a preliminary step necessary to develop milkfish fry

collections for aquaculture and has been done in Fiji and Kiribati (Bagarinao 1994a;

Billings et al. 2010). In Hawaii, a study conducted on the gonadosomatic index (GSI)

of milkfish over 36 months has indicated that breeding season is between June and

August with a synchronized spawning behaviour observed (Kuo et al. 1979). Among

the thirteen countries for which the seasonality of milkfish fry was established

(Figure 1.4), Fiji is the only one that lies along the same latitude of Vanuatu and thus

may help to predict the fry occurrence.

Figure 1.3 A graphicoccurrence in several(1986) and Vuto et al

1.7 Migration and m

The fry swimming ve

Bagarinao (1991) h

however, they becom

and distribute evenly

11

cal representation of peak and lean season of l countries with data retrieved from Kuo et al. (2014).

movement of fry

elocity is within the range of 9-11 cm/s (Kaw

has stated that milkfish fry near shore wat

me loosely aggregated. The fry arrive in batche

y along extensive sections of beach. There is

f milkfish fry al. (1979),Villaluz

wamura et al. 1984).

ters do not school;

es at different times

s a need for further

12

studies to determine mechanism of larval transport to understand the natural

recruitment of fry along inshore habitat (Bagarinao 1991). Some parameters that

influence the abundance of fry along the coast were discussed by Kumagai (1984)

such as currents, tides, bottom profile and proximity to inland waters whereby

currents and tides were the factors that influence most the abundance along the

shoreline. Fry are more abundant at flood tide due to the effects of the strong current

and collected in large numbers at the surf zone (Bagarinao 1991). The time of day

and wind speed does not have any influence on the fry abundance (Bagarinao 1991).

The arrival of fry at the shoreline is in the form of small batches and this movement

was suggested to be passive, driven by physical factors as such as longshore current

(Kumagai 1984; Villaluz 1986). Although Buri & Kawamura (1983) claimed that fry

in inshore waters were actively migrating into coastal habitat, Kawamura (1984)

suggested that migration was also passive towards nursery habitat. More recently,

Bagarinao (1994a) stated that, milkfish fry move inshore by both passive advection

and active migration.

1.8 Predation on milkfish fry

The most important predators of milkfish larvae and fry are the Hawaiian tenpounder

Elops hawaiensis and the Indo-Pacific tarpon, Megalops cyprinoides (Buri 1980;

Pickering et al. 2012). Other common predators of milkfish are Ambassis sp.,

Terapon sp., Epinephelus sp., Lutjanus sp., Sphyraena sp., Chaetodon sp.,

Meiacanthus grammistes, Oxyurichthys microlepis, and Scatophagus argus (Buri

1980). Bagarinao (1991) suggested that milkfish fry may be eaten also by mugilids

and siganids. The fry of tarpon and tenpounder are very similar to milkfish but they

are predators of milkfish fry and fingerlings. These two species can be distinguished

from milkfish as they have longer and wider bodies and much larger mouth, different

swimming movement and light amber colour (Villaluz 1986).

1.9 Overview of main methods of fry collection

13

Milkfish fry are well-captured using gears operated by filtering water, such as

plankton nets. Milkfish fry have well developed vision so they may respond

negatively (i.e. avoidance) if they recognize the gear or positively (driven) with the

gear if they see the net as some form of shelter (Bagarinao 1991). Black nets were

observed to be more effective in catching fry although white nets are preferred due to

easy identification of fry during capture (Kawamura et al. 1980). Experiments in

tanks on the behavior of the fry response to gear revealed that, milkfish fry gear with

herding design will function well rather than those with filtering (Kawamura et al.

1980). The good condition of the fry is identified through their ability to swim in one

direction facing the current (Villaluz 1984).

The selection of a more appropriate and effective method to collect milkfish larvae

or fry from the wild depends also on the topography of the site, currents, wind

direction and tidal fluctuation (Villaluz 1986). However, the effectiveness of the

methods can also be affected by small population size as shown in small lagoons

with small population (Buri 1980).The fry are caught better with driving gears than

filtering, and the gears may perform well in shallow part of the fry ground. It has

been reported that milkfish fry used to congregate close to the fish shelter located

offshore where they can be caught in sizable quantities (Villaluz 1986). The fry

always stay at the surface, even when they are scared so the depth of the catching

gear will not have to be increased to catch more fry (Villaluz 1986; Villaluz et al.

1983b). The gears used in fry collection are fine nylon nets with a mesh size ranging

from 0.3 to 1.6 mm. The bulldozer net method is a very useful fry collection gear,

which is normally operated in shallow lagoon. The bulldozer net gear was use first in

the Philippines and it was reported to be effective in the night (Villaluz 1986).

However, more recently, Vuto et al. (2014) showed that there is no significant

difference in density of fry between the day and night.

Milkfish fry swim at the low speed of 9-11 cm/s (Kawamura 1984). They are caught

in large numbers with juveniles and also the larvae of other predatory species

(Bagarinao 1991). Sampling methods used in different countries are selected based

on the topography of the sites, such as skimming net, hand scoop net, seine net

collector, beach drag seine net, push net or bulldozer, barrier net and plankton net

(Garcia 1990; Pickering et al. 2012). A skimming net is used in mud flats and

14

mangrove areas, and the hand scoop net is used mainly in mudflats, pools and canals.

The seine net collector is used mainly in mud flats. A beach drag seine net is used

mainly in deep waters of the shoreline. The barrier net is used mainly in estuaries

with bridge as deploy platform for high and low water influx (Villaluz 1984).

Plankton nets are used in deep waters and also on the bridge as a barrier for trapping

fry during high tide (Kawamura 1984). The best design for fry collection in sandy

beaches is the bulldozer net whereby one person will push the dozer net while the

other person will check the back of the net for fry using a plastic basin. The fine

mesh size net of 30 μm is used for collecting the fry constructed onto a bamboo

frame. The separation of the fry will be made in a white basin whereby milkfish fry

will be spotted as having two spot on the eyes, a fork tail, and a black spot on the

middle and the characteristic is of a darting swimming behavior into the current

when the water swirled (Pickering et al. 2012).

1.10 Food demand in the Pacific island countries

In the PICs and Territories, fish consumption is common and a major source of

protein food as many of the villages are located along the coasts. The average fish

consumption per capita in PICs and Territories is 16 -18 kg per person per year (Bell

et al. 2009). The decrease of protein food supply from the oceans is an ongoing

problem all around the world due to increased demand from the growing human

population, and aquaculture is deemed to be an efficient approach to address food

demand in the coming future (World Bank 2013). Capture fisheries have so far

contributed to food production, but unfortunately they are unable to supply the

growing demand as more people request fish and fish products (Tidwell et al. 2001).

Aquaculture alone has accounted for 47 % of fish supply as capture fisheries leveled

off in the last twenty years (FAO 2016) . Overfishing plays a major role in the

decline of coastal ecosystems (Myers et al. 2003) and climate change may play a

significant part as well (Williams et al. 2010). Research into aquaculture is

increasing globally to identify new approaches that may support food security and

sustain community livelihood through sustainable production. Different marine

species are studied which increases chances for potential later application in

15

aquaculture. Milkfish is one of the marine species farmed previously as traditional

industry in Asian countries where annual restocking of fingerlings was reared from

wild caught fry (Nelson 2007). The culture of milkfish was reported to spread to

some PICs and Territories, and the potential is recognized to address food demand

(Pickering et al. 2011). In Vanuatu, milkfish forms an extremely small component of

substance diet when compared to its multispecies fisheries. There has been a history

of collecting seasonal shoals of milkfish fry and juveniles for food (Pickering et al.

2012). In the Solomon Islands, milkfish aquaculture is based on fry collection from

the wild, and the economic analysis done by Sulu 2016 has confirmed that

subsistence farming is possible if labor cost is zero (Sulu et al. 2016). As such,

milkfish subsistence farming may be predictable also to contribute to subsistence diet

in Vanuatu. Moreover, reef fish is becoming very expensive in Efate, which is the

most populous island in Vanuatu and where the capital of Vanuatu is located,

therefore, if lower income households were able to culture milkfish this could

improve both their food security and culture options.

The Vanuatu government has recognized milkfish as a priority species for culture in

the Aquaculture Action Plan (SPC 2008), but no attempt has been made yet on

culturing the milkfish Chanos chanos species. In some PICTs such as Fiji, Kiribati

and Solomon Island attempted were made by collecting the fry from the wild for

culture based on the knowledge of the seasonality (Billings et al. 2010; Vuto et al.

2014; Wainwright 1982). The Australian Centre for International Agricultural

Research (ACIAR) funded project FIS/2012/076 – Improving community based-

aquaculture in Fiji, Kiribati, Samoa and Vanuatu, is now supporting the government

action plan. In this master’s thesis the seasonality of milkfish fry will be determined

as part of the plan for Vanuatu. Upon completion of this, the Vanuatu government

will have at disposal useful information for further work, such as trial culturing and

assessing the economic viability for milkfish culture. The knowledge of milkfish fry

seasonality is the primary basis of the aquaculture process where there is a lack of

advanced breeding technology, such as in the PICs and Territories. There has been a

history of collecting seasonal shoals of milkfish fry and juveniles for food (Pickering

et al. 2012) but to date there has been no attempt to quantify milkfish fry seasonality

in Vanuatu. Hence, the knowledge of milkfish fry seasonality and abundance is

important for further engagement in milkfish farming in Vanuatu.

16

1.11 Conclusion

The literature review has re-affirmed importance of quantifying the seasonality of

milkfish fry in Vanuatu in order to establish baseline information for fry collection,

which is a prerequisite for milkfish aquaculture development. Environmental

variables can also affect the fry seasonality and spawning time and density.

Temperature is known to be a variable that influences milkfish spawning. Milkfish

fry seasonality is latitude dependant with two peaks close to the equator and one

peak at higher latitudes. This chapter provided some knowledge of milkfish studies

in the past that will help to establish the seasonality study in Vanuatu. The methods

of fry collection, time of spawning, and other variables that influence fry appearance

and abundance were highlighted in the review. The methods for fry collection were

reviewed and the best method based on the topography of the sites will be adopted in

this study.

1.12 Research objectives

The main aim of this research is to determine the availability of milkfish fry and their

seasonality and abundance in a coastal area of Efate Island, Vanuatu.

The following is a list of questions that this study is addressing:

1. Is milkfish present in the selected study areas on Efate Island, Vanuatu?

2. What is the seasonality and abundance of milkfish fry in the selected study

area on the coast of Efate Island, Vanuatu?

3. What is the age of milkfish fry at the coast of Efate, Vanuatu?

There are three hypotheses to be tested:

1. Fry abundance in Vanuatu shows a lunar and annual seasonality

2. Environmental factors such as temperature, cloud cover, rainfall, wind speed,

current speed, and turbidity are correlated with fry abundance, length and

weight.

17

3. Fry abundance in the New Moon, 1st quarter Moon, Full Moon and 3rd quarter

Moon are significantly different.

The following is a list of objectives to answer the questions raised above.

1. To determine the presence, seasonality and abundance of milkfish fry at different

sites related to the Moon phase in the coastal zones of Efate Island.

2. To estimate the age at which fry appear along the coast of Efate Island.

3. To determine the impact of environmental variables on fry abundance, length and

weight.

18

Chapter 2: Methodology 2.0 Site selection and description

Efate Island is Vanuatu's third largest island and it is where the capital, Port Vila is

situated (Figure 2.1). Efate Island has the highest population due to migration of

people from the outer island in Vanuatu to Port Vila town for employment and

education (Amos 2007). A site inspection was conducted around Efate Island to

check for the eligible environmental characteristic such as presence of rivers,

lagoons, sandy shoreline, coral reefs, mangrove swamps and brackish shoreline for

fry occurrence. The Coast of Efate Island has bays and lagoons with mangrove

swamps and rivers. The fringing reefs are narrow and sandy beach is present in the

shoreline, as observed during site inspection. The river inputs into the lagoons create

turbid in shore water, which is preferred for milkfish fry recruitments. The four

closest sites to Port Vila were selected.

The four sites selected for the study were Erakor, Kawenu, Mele and Teouma

(Figure 2.2). Their coordinates according to Google Earth are as follows: Erakor:

17°46'54.04"S, 168°19'30.52"E, Kawenu: 17°43'49.30"S, 168°18'18.50"E, Mele:

17°41'31.02"S, 168°15'58.24"E, Teouma: 17°47'27.14"S 168°22'49.73"E. All the

four sites have input of freshwater from rivers and lakes into the coastal shorelines,

with Teouma having two rivers flushing into the lagoon, one from the East and the

other from the West. The similarities between sites were the coastal sandy beaches,

brackish water and coral reef within the lagoon. The differences were the size of the

lagoon, the source of fresh water (river and swamp), the presence and size of

mangrove canopy and the distance of the sites relative to Port Vila town (Figure 2.2).

19

Figure 2.1 Map of Vanuatu where the study is based. Retrieved from http://www.nationsonline.org/oneworld/map/vanuatu-map

20

Figure 2.2 Map of the four sites Erakor, Kawenu, Mele and Teouma where milkfish fry was assessed during the preliminary study, and the Vanuatu capital (marked with a star).

2.1 Sampling materials and methods

2.1.1 Sampling materials

A Secchi disk to test water turbidity was made from timber, and the rope on which

the disk was mounted was marked up to 100 cm with ±0.5 cm precision. A Kedida

concentration tester (CT) -3080 pen type salt and temperature meter were used to

measure salt concentration in mg/l with precision of ± 1 mg/l and temperature in

degree Celsius (°C) with ± 0.1 °C precision. A thermco water bath thermometer of ±

0.5 °C precision was used later to measure temperature during continuous sampling.

21

A plastic bottle, stop watch and a nylon rope of 5 m were used to measure current

speed along the surf zone of the coastline by deploying a plastic bottle and letting it

drift along a 5 m distance while taking the time with a stop watch. Additional

environmental parameters such as rainfall, cloud cover and wind speed were

obtained from the Vanuatu meteorology and Geo-hazard department (VMDG).

2.1.2 Bulldozer net construction

The bulldozer net was built from bamboo, and tire rubber was used to tie the bamboo

sticks together (Figure 2.3). The net was seamed with a 100 μm fishing line onto the

nylon rope to keep the edges from wearing and also to retain the shape. A wire was

used to attach the net at each corner of the frame and a fishing line was used to tire

the net into position. The pouch was a fine mesh size of 150 μm while the wings of

the net were made of a larger nylon mesh size of 250 μm.

The diagram of the frame with the measurements is shown in figure 2.4. The length

of the bamboo frame was 2.6 m and the back of the frame was narrow to allow for

easy pushing and collection of the fry. The front was wide which was used for the

wing controlling the fry.

The diagram of the net and measurement are shown in figure 2.5. The pouch was

short and covered about 1/3 of the total length. The back of the net was deep to

enable fetching when hauled to check for milkfish fry (Figure 2.5).

22

Figure 2.3 The bulldozer net built and used for this study. Picture shot at Teouma on March 2016.

Figure 2.4 The bamboo frame design for the bulldozer net (Pickering et al. 2012)

23

Figure 2.5 Net size and design modified from Pickering et al. (2012)

2.1.3 Sampling method

The net was first tested for its effectiveness and efficiency at the Kawenu lagoon

on the side towards Port Vila. The first deployment showed the catching of a

juvenile grouper after three trials pushing over 25 m along the surf zone.

Sampling trips were made once in every Moon phase for one-year period.

Overall, 69 sampling trips were made during the period of this study from

February 17th 2016 to February 15th , 2017 of which 18 trips were made for the

preliminary site assessment. A total of 7 to 8 net deployments were made per

sampling trip whereby each deployment covers a push over 25 m distance at a

time of 5-7 minutes. Each deployment is referred to as effort whereby the net was

checked for the fry presence for each deployment.

Fry abundance was checked in the surf zone. Net deployment was done only

during daylight hours between 6 am to 6 pm during the 1st and 2nd hour of high

tide. The abundance of larvae is expressed as number collected per effort

(Morioka et al. 1993) where the effort is the number of bulldozer net

deployments.

24

2.2 Fry identification

Milkfish fry identification was made visually with the help of a white plastic

basin on the field. Milkfish fry (Figure 2.6) is characterized by lack of

pigmentation, two dark spots (the eyes) on each side of the head, a dark spot (the

air bladder) on the middle of the body and also a light grey spot on the caudal

fin(Pickering et al. 2012). The fry uses a darting swimming motion with the

tendency to swim against the current.

Figure 2.6 Milkfish fry collected in a white plastic basin for visual identification. The black dot from left to right showed position of the grey spot on the caudal fin, dark spot in middle of body (air bladder) and two dark spot (eyes) on each side of the head.

2.3 Fry length and weight measurement

After identification, the larvae were dipped into 95% ethanol for 10 min to

enhance hardness for measuring and weighing. After 10 min, the TL of the larvae

was measured with a ruler and expressed in millimeters and weighed in grams

with an electronic balance (FX-1200 SN1010061) with a scale of 3 decimal

places and precision of 0.1 g. After mass and length measurements were done,

25

each larva was transferred into small containers of 20 ml in 95 % ethanol until

further use (Miller et al. 1994).

2.4 Otolith analysis

Before otolith analysis, a maximum of 5 fry from each sample collected in each

month was measured and TL measures were converted to equivalent fresh-state

using the equation from Morioka et al. (1993)on milkfish length conversion

applying the isopropanol equation. The equation for isopropanol was used as

there was none for ethanol available. The isopropanol equation employed was,

(Equation 2):

Equation 2:

Where TL is the total length of fresh specimen and Li is the length of the

specimen in isopropanol (Morioka, Ohno et al. 1993).

Examination of otolith was made on the sagittae on increment of Teouma wild

caught fry excluding the ones from Erakor, Kawenu and Mele, as the seasonality

study only focused on one site. A total of 91 fry was randomly selected from the

samples collected in Teouma for the examination.

The sagittae were removed from both sides of the milkfish fry cranium by teasing

them with an insulin syringe. Each sagitta was then mounted onto microscope

slides and immersion oil was used for otolith observation. Count of the total

number of increments was done under an Olympus dissecting light microscope

SZ-ST type of magnification ranging from 100 to 500x. The photos were taken

with an Infinity 1 canon camera (A-1) connected to the microscope and counts

were done twice, three days apart, by using the same photographs. A third count

was done under the microscope. The three counts were validated using analysis

of variances (ANOVA) single factor in excel and only the counts from the

microscope were used in the age estimate.

The age of milkfish was determined from the reading of otoliths. In milkfish the

first increment is formed two days after hatching during yolk sac re-absorption

period and the increments continue to grow daily regardless of the growth rate

26

(Bagarinao 1991). The relationship between the number of increments and the

age in days is the following (Equation 3):

Equation 3: D = N + 1

Where N = number of increments and D = Days from hatching

The equation, developed by Bagarinao (1991) was used to backdate the time of

hatching and thus the date of spawning was calculated from the counting done

under the microscope.

2.5 Data analysis

The comparison of milkfish fry abundance in the different sites, months and

Moon phases were determined using ANOVA in R version 3.4.0 (R Core Team

2007) with a significance level of 0.05. The difference in weight and length

between Moon phases was also determined by the same test. The fry seasonality

data was presented from August 2016 to January 2017 and from February 2016

to July 2016 to better depict the seasonal occurrence of milkfish fry.

The environmental data collected during sampling and those collected on

sampling day by VMDG were analyzed to evaluate their effect on the milkfish

fry abundance, length and weight. Regression analysis with multiple predictors,

also known as multiple regressions, was run and model selection was made by

comparing the most complex model with simpler ones in R for all variable data

such as sea surface temperature measured in situ, cloud cover, rainfall, turbidity

and wind speed. The Pearson correlation test for statistical software version 10

(Statistica Inc 2011) was conducted to verify the correlation coefficient and

significance level at 95% significance level and then used as final. Lastly the

correlation between age, length and weight of fry was done in Microsoft excel

version 15 (Microsoft Officer 2013).

27

Chapter 3: Results

A total of 47 fry were captured in the four sites altogether for the site assessment,

with 369 fry collected in the Teouma bay during a one year period and were used for

the following analysis except for aging, which was done on a subsample of 91 fry.

3.1 Site assessment and selection

Results for the four environmental parameters (i.e. turbidity, current speed, salinity,

and temperature) assessed over a month in Erakor, Kawenu, Mele and Teouma are

summarized in table 3.1. Erakor, Kawenu, Mele and Teouma, had a mean turbidity

of 80 ± 12.2 cm, 75.8 ± 10.3 cm, 89.3 ± 4.0 cm and 69.5 ± 11.2 cm respectively.

During the first 1-2 hour of high tide, Teouma had a mean current speed of 0.01 ±

0.0 m/s and Mele, Kawenu and Erakor of 0.01 ± 0.1 m/s. In ascending order

Teouma, Kawenu, Erakor, and Mele had mean salinity of 8.4 ± 2.5 parts per

thousand (ppt), 14.1 ± 3.0 ppt, 14.5 ± 3.5 ppt and 15.3 ± 3.5 ppt respectively. The

mean monthly sea surface temperature (SST) measured showed Mele had the lowest

(30.4 ± 1.7 C), while Teouma, Kawenu and Erakor had a higher temperature (30.7 ±

0.5 C, 31.1 ± 3.5 C and 31.3 ± 2.0 C, respectively).

Table 3.1 The monthly environmental parameters (turbidity (transparency), current speed, salinity and SST) assessed and the landscape features for Mele, Kawenu, Erakor and Teouma. The monthly values are presented as mean ± standard deviation.

Sites

Landscape

features

Turbidity

(transparency)

(cm)

Current

speed

(m/sec)

Salinity

(ppt)

SST

(ºC)

Mele Sandy beach,

coral reef, two

rivers

89.3 ± 4.0 0.1 ± 0.1 15.3 ± 3.5

30.4 ± 1.7

Kawenu Sandy beach,

coral reef, spring

75.8 ± 10.3 0.1 ± 0.1 14.1 ± 3.0 31.1 ± 3.5

28

water, mangrove

habitat

Erakor Sandy beach,

coral reef, lagoon,

swamps

80.0 ± 12.2 0.1 ± 0.1

14.5 ± 3.5

31.3 ± 2.0

Teouma Sandy beach,

coral reefs, two

rivers

69.5 ± 11.2 0.1 ± 0.0 8.4 ± 2.5 30.7 ± 0.5

Milkfish fry appeared in the four sites with the least abundance recorded in Erakor,

Kawenu and Mele (1, 2, and 1 fry, respectively) and was significantly different (p =

0.01) from those in Teouma with the highest (43 fry) (Figure 3.1). The lowest

number of fry at Erakor, Mele and Kawenu were not significantly (p > 0.99) different

from each other.

The study proceeded only in Teouma, based on low numbers of abundance in the

other sites. Thus, the following results refer only to Teouma.

29

Figure 3.1 Milkfish fry total abundance (number of fry captured during the exploratory trial done on Erakor, Kawenu, Mele and Teouma). The different letters indicate significant difference in abundance (p < 0.05) while the same letter indicates no significant difference (p > 0.05).

3.2 Milkfish fry occurrence in Teouma 3.2.1 Monthly occurrence and abundance

Milkfish fry occurrence in Teouma started in October and ended in early May

(Figure 3.2). The month of November and April showed the two highest peaks in

abundance (120 and 92 fry respectively) with no significant difference where p =

0.67 (Appendix 1). In the months of October, December, January, February, March

and May the abundance was low (19, 24, 3, 55, 41 and 15 fry, respectively) and

significantly different from those November (92) and April (120) where p < 0.05

(Appendix 1). The months of June, July, August and September showed no

occurrence of fry, but were not statistically different (p > 0.05) from the months with

low abundance October, December, January, February, March and May except for

July and February which were significantly different to each other where p = 0.03

(Appendix 1). The sea surface temperature (SST) collected from both Meteorology

department and in situ shows milkfish fry occurrence at monthly mean SST of 26℃

and above while no occurrence is observed at mean SST below 26℃.

30

Figure 3.2 Milkfish fry abundance and occurrence with SST by month for Teouma. The different letters indicate significant difference in fry abundance (p < 0.05).

3.2.2 Milkfish fry length and weight

The mean total length (TL) of the collected fry was 12.8 ± 1.2 mm (Appendix 3).

The Moreover, 59 % of the fry had length from 13 to 14 mm and 33 % had the length

between 11 and 12 mm (Figure 3.3). The minimum length recorded was 8 mm and

the maximum was 15 mm.

The weight of the milkfish fry ranged from 3 mg to 9 mg, with an average weight of

5.8 ± 1.6 mg (Figure 3.4, Appendix 3). A total of 65 % of fry in Teouma had a

weight range between 5 mg and 7 mg while 17 % of the fry caught had a weight of 8

mg and 9 mg.

The fry TL by months shows that May had the highest mean TL (Figure 3.5, A) and

is significantly different in April and October (p = 0.04 and p = 0.04 respectively)

with the lowest mean

sampling shows no st

Figure 3.3The total le

Figure 3.4 The frequ

31

n TL. The comparison of weight by month

tatistical significance (p > 0.05) with the weig

ength frequency of milkfish fry (N = 369) in th

ency distribution of milkfish fry (N = 369) we

h (Figure 3.5, B) of

ght of fry collected.

the Teouma

eight in Teouma

Figure 3.5 Milkfish frThe different letters inrepresent the standar

3.3 Effect of Moon p

3.3.1 Abundance by

The distribution of cu

showed that the highe

followed by 3rd quarte

the two (Figure 3.6).

Moon (N = 57 and 34

abundance in New M

in the 1st quarter and

0.12).

32

fry mean total length (A) and weight (B) per sndicate significant difference (p<0.05). The e

rd deviation of the mean.

phases

Moon phase

umulative fry abundance at the four consecuti

est fry abundance (N = 160) was observed du

er (N = 120), with no significant difference (p

Milkfish fry abundance was lower in the 1st

4 fry, respectively), and were significantly dif

Moon (p = 0.001 and p = 0.001 respectively). T

3rd quarter Moon phase were not significantl

sampling month. error bars

ive Moon phases

uring New Moon,

p = 0.44) between

quarter and Full

fferent from the

The fry abundance

ly different (p =

33

Figure 3.6 Milkfish fry cumulative abundance in all Moon phases for Teouma

throughout the year. The different letters indicate significant difference is the

abundance between Moon phases (p < 0.05).

3.3.2 Total length and weight in Moon phase over one year

The mean total length of the fry captured at 1st quarter, Full Moon and 3rd quarter

(13.1 ± 0.9 mm, 13.5 ± 1.0 mm and 13.1 ± 1.2 mm, respectively) were not

significantly different (p > 0.05) from each other (Figure 3.7.A, Appendix 1). The fry

in 1st, 3rd and Full Moon had a mean total length higher than the fry captured at New

Moon (12.2 ± 1.2 mm) and were significantly different (p < 0.05) from each other

(Figure 3.7).

The fry captured in the 1st quarter Moon phase had the lowest mean weight (4.7 ± 1.5

mg) followed by the Full Moon (4.9 ± 1.8 mg) and not significantly different (p =

0.61) from each other (Figure 3.7, B). In the 3rd quarter and New Moon the fry had

the highest mean total weight (5.3 ± 1.7 mg and 5.4 ± 1.6 mg, respectively) and these

were not significantly different (p = 0.10) from each other. The fry sampled at the

Full Moon had a mean weight not significantly different (p > 0.05) from the other

Moon phases (Appendix 1).

Figure 3.7 Milkfish frThe different letters s0.05) and the error ba

3.4 Comparison of f 3.4.1 Environmental

The environmental va

and current speed (ha

the coastal shoreline a

However, cloud cove

0.05) whereby fry abu

34

fry mean total length (A) and weight (B) in foushow significant difference in mean total lengars represent the standard deviation of the m

fry abundance with other indices

l variables correlation with fry abundance

ariables assessed (temperature, rainfall, turbid

ad no significant influence on the milkfish fry

as shown by the low correlation values (p > 0

er had a significant influence on the milkfish f

undance increased with cloud cover.

ur Moon phases. gth or weight (p < mean.

e

dity, wind speed

y abundance along

0.05) (Figure 3.8).

fry abundance (p <

Figure 3.8 The envirotemperature, turbidityabundance.

3.4.2 Environmental Milkfish fry length sh

cover, rainfall and tur

speed showed a signi

respectively) with fry

35

onmental variables, rainfall, cloud cover, winy (transparency) and current speed, correlate

l variables correlation with length and wei

howed non-significant correlations with temp

rbidity (p > 0.05) (Figure 3.9). The wind spee

ficant (p < 0.05) positive correlation (r = 0.24

y length.

nd speed, ed with milkfish fry

ight of milkfish fry

perature, cloud

ed and current

4 and r = 0.21,

Figure 3.9 The enviro(transparency), wind length

Milkfish fry weight s

cloud cover, wind spe

= 0.02) positive corre

transparency increase

36

onmental variables, temperature, cloud coverspeed and current speed correlation with mi

howed non-significant (p > 0.05) correlations

eed and current speed (Figure 3.10). There w

elation in milkfish fry weight with rainfall and

e.

r, rainfall, turbidity lkfish fry total

s with temperature,

as a significant (p

d turbidity as

37

Figure 3.10 The environmental variables, temperature, cloud cover, rainfall, turbidity (transparency), wind speed and current speed, correlation to milkfish fry weight

3.5 Otolith analysis and age of the fry per month and spawning estimates

The age of the fry was assessed by measuring the number of increments in the

otoliths. In figure, 3.11 are shown examples of this assessment. In more detail, the

increment of a young larvae of 14 days old (Figure 3.11, a) has wider rings indicated

with a series of black dots while older larvae of 22 days (Figure 3.11, c) have narrow

increments. The star at the center of otolith indicates the core which was formed

before the first increment and the discontinuity zone shown by the light zones

indicated with the bar (Figure 3.11, a). There are four dimensions on the otolith

sagittae (Figure 3.11, a) of a milkfish fry, the posterior, ventral, dorsal and the

anterior. The 3 photos (Figure 3.11, a, b, c) indicate a typical 14 days, 15 days and a

22 day old milkfish fry otolith increments.

38

Figure 3.11 Photographs a, sagittae otolith from 14 days old larvae, 11 mm total length (TL). (x400), b is an otolith of a 15 day larva of 11 mm TL and, c is an otolith of a 22 day larva of 14 mm TL. In photograph a, letters. A, anterior; P, posterior; D, dorsal; V, ventral. The dots (●) are the increment dark zone, the star ( ) indicates the core and the arrow (↓) indicate the discontinuity zone.

3.6 The age distribution

The milkfish fry at Teouma coast were of age that ranged from 13 days to 25 days

old (Figure 3.12). The fry age that ranged from16 days to 18 days accounted for 57

% of the total fry caught while 29 % of the fry were aged between 19 to 22 days.

39

Figure 3. 12 The age frequency of milkfish fry in Teouma coastal shoreline

The age distribution between months revealed by otolith analysis two distinct age

groups, the first from October to December and the second was from February to

May (no otolith analysis was performed with samples from January) (Figure 3.13).

The oldest fry appears in March, April and May.

Figure 3.13 The mean age of fry per month of occurrence in Teouma. The error bars represent the standard deviation of the mean.

40

The relationship between total length and age shown in figure 3.14 indicates that the

length was directly proportional to the age where r = 0.46. Thus length also increases

with age at occurrence of fry and were significantly correlated (p < 0.05).

Figure 3.14 Correlation between the age and length of milkfish fry 3.7 Spawning time estimates for Teouma over one year period The backdating of the otolith data for each sampling trip revealed that milkfish-

spawning season starts in September and ends in April (Figure 3.15). Moreover,

there were two spawning groups or seasons, one from September to November and

the other from January to April. Milkfish spawning does not occur in December,

May, June, July and August. It is observed that milkfish spawning activity in

Teouma is link to the mean Monthly SST of above 25 ℃, and is the predicted

spawning threshold (Figure 3.15).

41

Figure 3.15 The spawning season of milkfish fry (N =63) based on different days over a one year period with mean Monthly SST

3.8 Comparison of fry abundance in the Melanesian PICs

The fry abundance in Teouma for one day over 1 hour of sampling using

bulldozer net is very low (0-79 fry) compared to the fry abundance reported in

Fiji and the Solomon island with 200-100 and 0-1000 respectively over one day

of sampling (Table 3.2).

Table 3.2 The fry abundance between Fiji, Solomon Islands and Vanuatu

42

Chapter 4: Discussion

The main goals of this study were to identify milkfish fry seasonality, abundance,

and spawning season, and to identify the environmental parameters such as Moon

phases, cloud cover, current speed, rainfall, turbidity, temperature and wind speed for

their effects on milkfish appearance and abundance in Vanuatu. The knowledge of

fry seasonality is crucial for Vanuatu, as hatcheries are too expensive to operate due

to the high cost of induced spawning technology, bloodstock hatchery, and

management. Similarly, according to FitzGerald (2004), the high cost of capital

investment along with investment on technically trained staff will make the

development of hatchery not advisable in the initial stage of milkfish aquaculture.

Therefore, the study can aid policy implementation based on this information for

milkfish culture purposes in Vanuatu.

Initially, four sites close to Port Vila on Efate Island, namely Erakor, Kawenu, Mele,

and Teouma were selected for a preliminary assessment. The sites were selected due

to the presence of rivers, freshwater sources, and landscape features such as a lagoon,

sandy beach, coral reef and coastal mangrove forest. The presence of rivers and

lagoon creates favorable environmental conditions known to be important for

milkfish fry appearance (Bagarinao et al. 1987; Bagarinao 1991; Brian 2015). All the

selected sites have similar topographic features of a gentle slope on the surf zone

whereby a bulldozer net method of fry collection was selected as it was used for the

first time in the Philippines in 1983 and was deemed effective along surf zones of

sandy coastal shorelines (Villaluz 1986). The pushes are made parallel to the

coastline facing the direction of the wind. The bulldozer net design used in this study

was a modification from the one used by Pickering et al. (2012). In Vanuatu, the

bulldozer net was never previously used for any purpose and that includes milkfish

fry collection, nevertheless, sampling done with the bulldozer net was proven

efficient in this study and thus its further use is highly recommended in locations

with similar characteristics.

After the completion of one-month assessment in the four sites, it was observed that

milkfish fry was present in all four sites. However, Erakor, Kawenu, and Mele, the

43

sites closest to Port Vila, had the lowest abundance in milkfish fry. Teouma was the

site furthest from Port Vila where the council of chiefs has control of the coastal

resources. Recently they imposed regular seasonal banning of fishing from

November to April as they believe it is the season when much of the spawning

occurs. In Pakistan, a study on the breeding season of Schizothorax plagiostomous

by Jan et al. (2017) using GSI techniques resulted that spawning occurs twice a year,

once in March-April and October-November. Similarly, an evaluation of closed area

for fish stock conservation in Europe by Horwood et al. (1998) revealed that closure

areas were likely to have benefited many commercial and unregulated fisheries

species. In addition, a study of the sustainability of two coral reef fish (Amphiprion

percular and Chaetodon vagabundus) larvae recruitment in a Marine Protected Area

(MPA) in Papua New Guinea revealed that even small MPAs may be self-sustaining

in larvae recruitment from the adult spawning in the same location (Berumen et al.

2012). This may be the same case for the seasonal closure in Teouma where adult

milkfish around the coast will only sustain fry recruitment along the Teouma

shoreline. However, this needs to be verified with a more comprehensive research. In

addition, the presence of two rivers within the lagoon in Teouma also makes a good

fry collection ground. This is similar to what was found by Sulu et al. (2016) in the

Solomon Island that better fry collection grounds are usually located close to river

mouths and swamp outlets. Furthermore, Bagarinao (1991) has stated that the most

important component of the water chemistry is the muddy smell, composed of

organic compounds called geosmin which is formed from the bacterial breakdown of

detritus and benthic zooplanktons that triggers most of the fry appearance to the

coastline to feed where conditions are favorable.

The physical parameters of turbidity, current speed, salinity, and temperature, were

measured at sampling during the site assessment and some differences between the

sites were recorded, that may aid to explain the differences in milkfish fry

abundance. It was evident in Teouma that physical parameters such as temperature,

current speed, turbidity, and salinity do not fluctuate when compared to the other

three sites Erakor, Kawenu, and Mele. The stability of the environmental conditions

is crucial for milkfish larvae survival, similarly, the high survival rate of milkfish

44

juvenile was observed by Jaspe et al. (2012) in the pond when there is enough food

supply and water quality is stable.

Milkfish fry appearance in Teouma started in October and continued to occur until

early May which is similar to their occurrence in Fiji from September to May

(Pickering et al. 2012) and has two peaks which are similar as in the Solomon island

(Sulu et al. 2016). A study on the gray mullet Mugil cephalus fry seasonality in

South Africa by Bok (1979) revealed that recruitment along the coastline occurs

from May to November and the peak period of occurrence took place from July to

October. The seasonality of Mugil cephalus in South Africa is different to milkfish

fry occurrence in Vanuatu. In India, Sarojini (1951) has determined that the fry of

Mugil tade and Mugil parsia usually occur from November to February (Oren 1981).

On the Teouma coast of Efate, milkfish fry recruitment had two peaks of occurrence,

one in November and the other in April (120 and 94 fry respectively) which is

similar to the number of peaks recorded in Kiribati although the peaks were shorter

compared to Kiribati with peaks from May to September and December to April

(Wainwright 1982). However, fry seasonality in Kiribati is similar to those of

Solomon Islands (Sulu et al. 2016), as it occurs throughout the year, which is

different to Fiji and Vanuatu with 8 and 9 months respectively. In October,

December, January, February, March, and May a low number of milkfish fry was

observed in Teouma. The months of October and January were the beginning of the

first and second period of fry seasonal appearance, which later leads to the peak

occurrence in November and April. The reduction in fry abundance in March may be

related to the effects of storm surge due to cyclone Winston which started early in

February in North West of Port Vila in Vanuatu. Similarly, a visual census carried

out in 8 coral patch reef in Lizard Island of great barrier reef during larval seasonal

peak occurrence 12 days before and 2 days after a cyclone resulted in fewer juveniles

recruited into the coral reef due to storm surge (Lassig 1983). The study has

concluded that cyclone has marked effects on the fish assemblage as a whole. In

Teouma, the sampling done 2 days after the week of storm resulted in no fry and

they become available only on the sampling day, which is 10 days after the storm

surge of the cyclone. Therefore, the larvae could have suffered additional mortality,

45

which resulted in a decline of fry abundance in March. No fry was captured in the

months of June, July, August, and September. The close range in length of fry

occurrence in Fiji and Vanuatu may be related to the closeness in latitudinal position

between the two countries as it was stated that countries with similar latitude would

have similar periods of occurrence (Bagarinao 1994b). Milkfish fry in the coastal

shoreline of Teouma occurs mainly in the summer months, which may be the same

for their occurrence reported in Fiji. However, the low abundance observed in this

study could also be related to sampling chance, as there is no significant difference in

abundance in the month of low fry occurrences and those of no fry occurrence. A

different method of sampling is required to avoid errors in sampling chance as in the

Solomon Islands and Fiji more fry was caught using other methods (hand dip net,

scoop net) in narrow, shallow lagoon compared to bulldozer net (Sulu et al. 2016).

By comparing the fry abundance in Teouma to Fiji and Solomon Island’s data, fry

abundance in Teouma (0-79 fry per hour) may not be so different using the bulldozer

if sampling is done for more than one hour per day. In Fiji and Solomon islands, fry

were collected at 200-1000 and 0-1000 fry in a sampling day respectively (Napulan

2012; Sulu et al. 2016).

Milkfish fry TL for Teouma coast ranged between 8 mm and 15 mm. This is similar

to those appeared in Japan and Philippine which ranged from 10 mm to 17 mm

(Kumagai 1984; Senta et al. 1981), however, they are more similar to those occurred

in Solomon island with a length range of 10 mm to 15 mm (Sulu et al. 2016). In the

Philippines, milkfish larvae of less than 9-10 mm TL are present in offshore surface

waters but are driven onshore by wind-driven current and tidal current (Kumagai

1984). The weights of the fry in Teouma ranged from 3 mg to 9 mg and were similar

to those reported in Taiwan by Liao et al. (1977) with the weight range from 3.2 mg

to 11.2 mg. In regards to seasonal abundance, milkfish fry was abundant in summer

compared to winter. The two peaks in fry seasonality were in line with previous

findings (Kumagai 1984), where it was determined that fry seasonality is long near

the equator with two peaks of which April-May is higher and progressively shorter at

high latitudes. The fry seasonality in Teouma occurs at monthly mean sea surface

temperature (SST) above 25℃ (figure 3.2) and most spawning activity also occurred

46

at temperatures above 25℃, similarly, milkfish fry occurrence in Fiji, Solomon

Islands, and Kiribati occurs at the same temperature (Bagarinao 1991; Sulu et al.

2016). Therefore, the SST threshold value for prediction of milkfish fry occurrence is

25℃ and above and is noted in the Philippines (Bagarinao 1991).

The milkfish fry occurrence in the different Moon phases showed a high frequency

in New Moon and 3rd quarter Moon phase (120 and 94 fry respectively). This

pattern observed in Teouma was different to the pattern of fry occurrence determined

in the Philippines whereby spawning occurs in quarter Moon period and fry are most

abundant in Full and New Moon period (Bagarinao 1991; Kumagai 1984). In

addition, in the Solomon Islands, the catch during the New Moon period is higher

than the Full Moon, which is similar to those observed in Teouma but a non-

significant difference was identified (Sulu et al. 2016). It was anticipated by Garcia

(1990) that milkfish fry is more abundant between full Moon and New Moon periods

after observing the seasonality of fry in the Philippines. However, this study carried

out in Vanuatu supports that fry is more abundant in New Moon period than in the

Full moon period. This is different to what is observed in Solomon Island and in the

Philippines. A study conducted by Horký et al. (2006), on the behavior of fish in

Moon phase using pikeperch, in the behavior revealed that New Moon has increased

diurnal activity compared to other Moon phases, similarly as the sampling was done

during the day, more fry was caught in New Moon. The results of this study also

show that smallest fry are more abundant in quarter moon period and otolith analysis

also proved that younger fry occurs in the similar period. Concerning the weight of

the fry in Moon phases, those fry appeared in New Moon have more weight.

According to Horký et al. (2006), fry activities increase in the New moon period.

This study supports that as fry activity increased in New Moon period, feeding could

also increase which result in more weight of fry in New Moon.

The environmental variables assessed (temperature in situ, rainfall, turbidity, wind

speed and current speed) had no significant influence on milkfish fry abundance

along the coastal shoreline of Teouma. The monthly mean SST (figure 3.2, 3.15)

indicates a possible link with fry seasonality although there was no correlation, and

this may need further assessment to validate. Fry were caught only on the months

when monthly mean SST was above 25 ℃ and this could be the threshold for

47

prediction fry occurrence. Similarly, countries like Fiji, Solomon Island and Kiribati

have records of fry occurrence at monthly mean SST above 25℃ (Bagarinao 1991).

However, cloud cover had a significant influence on milkfish fry abundance whereby

fry abundance increased with cloud cover that may reduce fry capability of seeing

and escaping the net. It was also noted by Kawamura (1984) after testing fry

visibility with black and white net mesh that fry escape white net mesh while they

retain more in the black mesh net. Nevertheless, a white color net mesh was used in

this study to ease milkfish fry identification, and as a result, fry tends to be caught in

higher numbers during high cloud cover possibly because net visibility is reduced. In

future studies, a black net should also be tested in Teouma to address the low capture

numbers and evaluate if these are related to the color of the mesh used.

The correlation of environmental variables studied with the length of fry over one

year period revealed that milkfish fry length was not significantly correlated with

temperature, rainfall, turbidity and cloud cover. However, wind speed and current

speed showed a significant correlation whereby larger fry were caught with

increasing wind speed and current speed. The wind speed drives fry into the net by

blowing onto the surface current causing larger fry difficulty to escape the net as the

net was deployed facing the wind direction. It was also reported in the Philippines

that milkfish fry were more abundant in favorable wind direction, particularly when

the wind blows towards the shoreline (Senta et al. 1981; Villaluz et al. 1983b).

The environmental variables, temperature, cloud cover, wind speed and current

speed, showed no significant correlations to milkfish fry weight. However, there was

a significant positive correlation of the fry weight to rainfall and increased turbidity.

Rainfall is important to fry as it increases river flow, causing suspension of detritus

in the coastline where more zooplanktons feed on them. Similarly, Edwards (2001)

has determined that zooplankton feeds on detritus and as more zooplanktons are

available, the fry feeding activity increases and thus the weight increases. In

addition, rainfall increases saturated oxygen concentration (Li et al. 2015), whereby

it was determined by Mallya (2007) using a case study on Atlantic halibut cultured

under various saturated oxygen concentration whereby growth and feed conversion

increase with saturated oxygen.

48

The age of the milkfish fry were assessed by measuring the number of increments

from 92 milkfish larvae. The fry (8-15 mm TL) captured on Teouma coast were of

age ranging from 13 days to 25 days old which is similar to the one determined in the

coast of Japan documented by Kawamura et al. (1984) where milkfish fry within 10 -

17 mm TL were aged between 14 to 29 days. Similarly, the fry result from Teouma

showed that more fry were aged between 16 and 18 days old which is not different to

those determined by Kawamura et al. (1984) whereby the fry length 12.5 -14.0 mm

TL were aged 18 to 21 days old. The result of the study revealed that milkfish fry

spend 2 to 4 weeks before disappearing for the nursery which correspond to the size

at transition stage reported by Bagarinao (1991). The fry length was positively

correlated to age, similarly, (Sackett et al. 2013) have stated that fish length increases

with age.

The spawning season of milkfish fry was determined by backdating of the otolith

data and revealed that milkfish spawning starts in September and ends in April, this

links to the period of fry occurrence mentioned previously in the first section,

whereby fry occurs in October following the spawning activity in late September.

Furthermore, there were two spawning groups or seasons, one from September to

November, and the other from January to April, which relates to the two peaks of fry

occurrence. The peak period of fry occurrence is short in the two periods of

spawning season. Helfman et al. (2009) found that typically pelagic fishes spawn

over a 4 month period with a short period of maximal activity, after determining the

spawning period of Cod in the North Sea of the Southeast coast of England where

spawning occurs between January and May where 70% of eggs produced during 6

weeks period. Milkfish spawning in Vanuatu does not occur in December, May,

June, July, and August. According to the results of the backdating, there is a period

of 44 days lapse between the first phase of spawning and the second phase of

spawning activity. The spawning season of mullet in Australia was studied by Horký

et al. (2006) who determined that Mugil chepalus spawning occurs between March

and September which is different to that of milkfish Chanos chanos in Teouma coast

of Vanuatu. The Mugil cephalus of the Mediterranean shore of Israel spawn from

July to December (El Meseda et al. 2006). It is seen that different species of mullet

spawn at different times of the year based on salinity and geographical location as

determined for Mugil cephalus (El Meseda et al. 2006). Similarly, Martinez et al.

49

(2006), has reported that different localities have different milkfish spawning seasons

whereby spawning can occur more than once during the annual spawning season. In

addition, an oocytes analysis of a hormone-induced trial on milkfish by Lee et al,

(1986) indicated that milkfish can spawn several times during the annual breeding

season (Garcia 1990). The otolith analysis resulted that some months fry appear

onshore were then to be older. The cause of the difference in age maybe related to

many factors.

Otolith analysis revealed that fry caught in November and February had the lowest

mean age. Older fry were caught in two periods, the first was in December and the

second period was in March and April. Further research is needed to determine

factors correlated to differences in fry age between the months of occurrence.

However, by synthesizing data from both seasonality of fry occurrence, age and

spawning period, it may be possible that this data can be used for management

purposes to predict fry seasonal occurrence. The months when occurrence peaks can

be used to determine abundance in other islands and possible fry collection ground

may need to be banned from catching of milkfish during the breeding season.

Therefore, milkfish aquaculture development in Vanuatu can be enhanced with this

knowledge of fry seasonal occurrence.

50

Chapter 5: Conclusion

This study has concluded that milkfish fry is available along the coast of Efate Island

in Vanuatu and it was present in all four sites assessed, though the abundance

recorded was low and thus unlikely to be sufficient to support milkfish aquaculture.

The sites close to Port Vila, Erakor, Kawenu and Mele showed low abundance in

milkfish fry compared to Teouma, which is the furthest site from Port Vila and was

selected for the seasonality study. The season of milkfish fry occurrence on the

Teouma coast of Efate started in October and ended in May, with two peaks of

occurrence identified, one in November and the other in April. The fry occurrence

was correlated with the spawning, which probably occurred from September to

November and from January to April, as inferred from aging analysis. Since the

study was done in the central province of Vanuatu, it is recommended that further

assessment of milkfish fry should be carried out also in other islands where

conditions are favorable for their occurrence.

The abundance of wild fry collected over the period of this study may not be

sufficient to support a subsistence culture of milkfish, as the numbers were quite low.

A comprehensive assessment of the abundance and seasonality is needed across the

Vanuatu groups of islands for the presence of milkfish fry and their occurrence in

order to close the seasonality of occurrence in Vanuatu and other methods of fry

collection may also needed to be tested on the abundance. A thorough study on fry

abundance will help determine whether milkfish culture in Vanuatu can rely on the

collection of fry from the wild. Additionally, the absence of fry in some months

could also be related to sampling chance, as there is no significant difference in fry

abundance between the month of low occurrence and absent. Most of the

environmental variables did not correlate with abundance, length, and weight of

milkfish fry, which may require further research to prove. Concerning Moon phases,

fry were more abundant in the 3rd quarter and New Moon compared to 1st quarter

Moon phase and Full Moon.

The period of fry occurrence is 8 months long, which is similar to that of Fiji.

However, the fry abundance was too low so the aquaculture of milkfish is still a

question that needs further research although the seasonality can be predictable. A

51

nationwide assessment can be done using this study as a pilot for spawning and fry

occurrence. The island of Santo, Malekula and Tanna would be the other sites that

look promising for the assessment, as there is plenty of bay and rivers connected to

the sea. However, it is recommended that after a complete assessment the seasonality

study should be done repeatedly over years to be able to build a complete cycle of

milkfish fry occurrence in Vanuatu.

52

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66

Appendix

Appendix A. Table of p-values for the ANOVA test

The following data were tested with ANOVA for the level of significance in R- software Sites Compared

to Milkfish fry abundance (number)

Significance level = p-value (95%)

Kawenu Erakor 1.00 Mele Erakor 1.00 Teouma Erakor 0.00 Mele Kawenu 1.00 Teouma Kawenu 0.01 Teouma Mele 0.01 Month Compare

to Milkfish fry abundance (number)

Significance level = p-value (95%)

January November 0.00 February November 0.02 March November 0.03 May November 0.00 October November 0.00 December November 0.00 January April 0.00 February April 0.00 March April 0.00 May April 0.00 October April 0.00 December April 0.00 November April 0.67 October June 0.99 December June 0.94 January June 1.00 February June 0.16 March June 0.27 May June 1.00 October July 0.96 December July 0.82 January July 1.00 February July 0.03 March July 0.08 May July 0.99 October August 0.98 December August 0.89 January August 1.00 February August 0.08 March August 0.17

67

May August 1.00 October September 0.98 December September 0.90 January September 1.00 February September 0.08 March September 0.17 May September 0.99 Month Compare

to Milkfish fry length (mm) Significance level = p-value (95%)

January April 0.89 February April 0.02 March April 0.59 May April 0.03 October April 0.92 November April 0.04 December April 0.38 January December 1.00 February December 1.00 March December 1.00 May December 0.95 October December 0.17 November December 1.00 January February 1.00 March February 0.96 May February 0.97 October February 0.03 November February 0.99 March January 1.00 May January 1.00 October January 0.68 November January 1.00 May March 0.67 October March 0.29 November March 1.00 Month Compare

to Milkfish fry weight (mg) Significance level = p-value (95%)

January April 0.67 February April 1.00 March April 1.00 May April 1.00 October April 0.28 November April 0.61 December April 0.98 January December 0.91 February December 1.00

68

March December 0.96 May December 1.00 October December 0.96 November December 1.00 January February 0.97 March February 1.00 May February 1.00 October February 1.00 November February 1.00 March January 0.62 May January 0.79 October January 1.00 November January 0.91 May March 1.00 October March 0.28 November March 0.69 Moon Compared

to Milkfish fry abundance (number)

Significance level = p-value (95%)

Full 1st moon 0.86 New 1st moon 0.01 3rd Moon 1st moon 0.12 New moon Full moon 0.00 3rd Moon Full moon 0.02 3rd Moon New moon 0.44 Moon Compared

to Total length for fry (mm)

Significance level = p-value (95%)

Full 1st moon 0.60 3rd Moon 1st moon 0.10 New moon 1st moon 0.00 3rd Moon Full moon 0.30 New moon Full moon 0.00 New moon 3rd moon 0.00 Moon Compared

to Total weight of fry (mm)

Significance level = p-value (95%)

Full 1st moon 0.29 New moon 1st moon 0.00 3rd moon 1st moon 0.00 New moon Full moon 0.53 3rd moon Full moon 0.61 3rd moon New moon 1.00

Appendix B. The daily

median and standard

2017.

69

y SST from VMDG and monthly mean, maxim

d deviation beginning from February 17th 201

mum, minimum,

16 to February 17,

70

Appendix C. Milkfish fry mean length and weight plus the descriptive statistic for

Teouma over one year period

Descriptive statistics

Length (mm) Weight (mg)

Milkfish fry Mean 12.8 5.78 Standard Error 0.1 0.08 Median 13.0 6 Mode 13.0 5 Standard Deviation

1.2 1.6

Sample Variance 1.5 2.5 Kurtosis 0.4 -0.5 Skewness -0.6 0.2 Range 7 6 Minimum 8 3 Maximum 15 9 Sum 4709 2135 Count 369 369