reproductive biology of blue tang fish ( paracanthurus...

Indian Journal of Geo Marine Sciences

Vol. 47 (04), April 2018, pp. 839-845

Reproductive biology of blue tang fish (Paracanthurus hepatus Linnaeus, 1776) in

Khanh Hoa seawater, Viet Nam

Huynh Minh Sang* & Ho Son Lam

Aquaculture Department - Institute of Oceanography, Vietnam Academy of Science and Technology,

01 Cau Da, Nha Trang, Viet Nam *[Email: [email protected]]

Received 23 August 2016 ; revised 28 November 2016

Blue tang fish (Paracanthurus hepatus Linnaeus, 1776) is one of the most popular fish caught in Khanh Hoa seawaters

for aquarium. A study on reproductive biology was conducted to evaluated the reproductive parameters including gonadal

development stages, sex ratio, spawning season, fecundity and size at first sexual maturity. Results showed that, number of

male and female in the nature was not significantly different. Gonadal of the fish passed through five stages of maturation.

The histological screening of gonad, percentage of maturation stage and gonadal somatic index value of the fish showed all

year round spawning with a peak of spawning female from April to September. Length at first sexual maturity of the fish

was 149.2 mm. Fecundity ranged from 1.527 – to 20.618 ovaries/ and strongly related to weight and length.

[Key word: blue tang, Paracanthurus hepatus, reproductive biology, Khanh Hoa]

Introduction The reproductive cycles of fishes are closely tied to

the environmental changes particularly temperature,

photoperiod and food supply1. Reproductive

parameters, such as gonadal development stages, sex

ratio, sex at first maturity, spawning season,

fecundity, are of great value in fishery resource

management and also essential and important in

aquaculture practices. The availability of quality seeds

and the ability to control fish reproduction are widely

recognized as limiting factors in the farming of any

commercial species2.

Blue tang fish (Paracanthurus hepatus Linnaeus,

1776) is a species of Indo-Pacific surgeonfish. This

fish is found from East Africa to Micronesia, Line

Islands and Samoa Islands, northwards to Kochi

Prefecture, southwards to New South Wales,

Australia. As a popular fish in marine aquarium, and

it is the only member of the genus Paracanthurus. The

species' range is broad, but it is common nowhere.

The fish can be found throughout the Indo-Pacific. It

is seen in the reefs of the Philippines, Indonesia,

Japan, the Great Barrier Reef of Australia, New

Caledonia, Samoa, Florida, East Africa, and Sri

Lanka, Vietnam. The blue tang is one of the most

common and most popular marine aquarium fish all

over the world. They live in pairs, or in small groups

of 8 to 14 individuals. These fish reach sexual

maturity at 9–12 months of age3.

Increasing demand for ornamental purposes of the

blue tang fish have been affecting in the natural

resource of this fish in Khanh Hoa seawater. A survey

data conducted to evaluation the natural caught of this

fish in Khanh Hoa has shown that total number caught

per year did not exceed 1000 individual4. Thus, there

is a great need for a suitable management strategy of

the natural resource of the fish as well as the strategy

for also breeding of this fish supporting for

ornamental aquarium, reducing the impact on natural

resource. However, information available on the

reproductive biology of this fish in Khanh Hoa

seawaters is still unknown. Hence, a detail

investigation on reproductive biology including

gonadal development stages, sex ratio, spawning

season, fecundity and size at first sexual maturity was

conducted and the results are presented and discussed

in this paper.

Material and Methods

Blue tang fish was collected from the fishing boat

fishing in Nha Trang bay and Spattly Island, Khanh

Hoa seawater from January 2015 to December, 2015.

The fish boat used trammel net, diving catch to collect

the fish. The size of fishes ranged from 30 to 180 mm

INDIAN J. MAR. SCI., VOL. 47, NO. 04, APRIL 2018

840

in total length. Around 30 fishes was collected each

month. The number of fish collect each month is

presented at Table 1.

The fishes was transported to laboratory at the

Institute of Oceanography, Vietnam for analysis. At the

laboratory the fishes were killed using ice-slurry

immersion method then weighed and measure the

length. Reproductive gonad of the fish (testes or ovaries)

were then dissected and weighed for further analysis.

While the maturity stages of females were

recognized based on the macroscopic appearance of

the ovary in the body cavity and microscopic structure

of ova, in males only the macroscopic appearance of

testes was considered. Gonadal development stages of

fishes were determined by methods of Nikolsky5 and

Xakun & Buskaia6 using Olympus BX50 microscope

at 10 X and 40 X magnification.

Histological analysis of testes and ovary was

performed following the method described by Gen

et al. (2007). Ovary or testes of each gonadal

development stage of fish were dissected and fixed in

4% buffer formalin for 24 h. After dehydrating by

passing the tissue through a series of alcohol solutions

of 70, 85 and 98%, the samples were vacuum

embedded in paraffin. The histological sections

(4 -5µm) were stained for general morphological

purposes with hematoxylin and eosin (H&E). The

samples were photographically analyzed and

documented using the Olympus BX 50 microscope at

40 X magnification.

Spawning season of the species was determined

based on the availability of mature and spent

individuals in the commercial landings during different

months and the monthly gonado-somatic indices (GSI).

The GSI was calculated7&8

using the formula:

GSI = 100 * (GW/BW) where GW is weight of gonad

and BW is weight of fish.

To estimate the length at first maturity (Lm), females,

were grouped separately into 6 mm class intervals and

fish in stage III and above were considered mature.

Length at first sexual maturity (Lm) were defined as the

length at which 50 per cent of all female fish having

ovaries at advanced stage of development according to

King9. The proportion of the female fish have ovaries at

advanced stage of development (P) of each size group

was adjusted by correction factor as the the biggest size

group was 100%. The linear relationship between size

group and Ln(1-P/P) was determined and the Lm was

calculated at P = 0.5.

Sex ratio was determined by the ratio of number of

male and female. Chi-square test was used to test the

different between the number of male and females in

the natural population of the fish.

To estimate fecundity, 30 ovaries in stage – IV

were utilised. From formalin preserved ovary of

known weight, a small portion was removed and

weighed to the nearest 0.001 g in an electronic

balance and then kept in modified Gilson’s fluid10

for

two days. All the oocytes in the sample ovary were

counted under binocular microscope using a counting

chamber. The absolute fecundity was estimated using

the formula: Absolute Fecundity (F) = (weight of

ovary/weight of sample) x number of oocytes in the

sample. The relationship between fecundity and total

length and weight statically determined using the

following formula: LogF = aLogX + b where F is

demoted fecundity, X is total length or weight, a and

b are constant. Relative fecundity was calculated

using the following formula: S=F/W where S is

relative fecundity W is fish weight (g).

Results The maturity stages of ovary and testes of blue tang

fish in Khanh Hoa was represented as in Tables 2 and 3.

Table 1 — Number of fish collected each month during 2015

Month No Month No

Jan 30 Jul 31

Feb 30 Aug 30

Mar 30 Sep 37

Apr 31 Oct 30

May 32 Nov 30

Ju 32 Dec 30

Table 2 — Maturity stages of female blue tang fish in Khanh Hoa

Maturity stages Particular of the gonads

Stage I, Immature Ovary was thin, short and glassy in appearance. It could not be distinguished ovary and testes by snake-eyes.

The stages was observed in the fish size under the first maturation size.

Stage II, Maturing Ovary developing, ovary and testes can be distinguished by snake-eyes. Ovaries are opaque and creamy

yellow.

Stage III, Mature Ovaries increase the size comparing to stage II. Ovaries are reddish yellow, extending about 2/3 body cavity

length.

Stage IV, Ripe/Oozing Ovaries are yellow to amber colored filling the entire body cavity, extending in the entire body cavity length

Stage V, Spent Ovaries are rather flaccid, reddish yellow.

SANG & LAM et al.: BIOLOGY OF BLUE TANG FISH (PARACANTHURUS HEPATUS LINNAEUS, 1776)

841

The histology of ovaries and testes of the blue tang

fish in Khanh Hoa are presented as Figs. 1 and 2.

Ratio of male and female of blue tang fish in

Khanh Hoa seawaters was 1:1,07. Number of male

and female was not significantly different (χ2 = 0,

45 < 3, 845 (df = 1, P < 0,05)).

The fishes at mature (III) and ripe stages (IV) of

ovaries presented all year round. However,

percentages of fish at maturation stages of III, IV and

V was higher during the priod from March to August

than that during the period from September to

February (Fig. 3). Percentages of advance stage of

ovaries (IV and V) in July was the highest (81 %) and

the lowest was in January 47 (%).

GSI of the female blue tang fish in Khanh Hoa

seawater was highest in March (0,65 ± 0,24), and

lowest was in October (0,22 ± 0,08). For the male

blue tang fish, the highest GSI was in February

Fig. 1 — Histological sections of ovaries of the blue tang fish in Khanh Hoa

Note: A, B, C & D is the histological section of the ovaries at II, III, IV & V maturity stage, respectively; Evtg: early vitellogenic oocyte;

AVtg: advanced vitellogenic oocyte; PG: primary growth oocyte; y: yolk vesicles; n: nucleus.


842

(0,22 ± 0,13) to April (0,22 ± 0,1), and the lowest GSI

was observed in October (0,14 ± 0.04) (Fig. 4).

The length of the first sexually maturity of the blue tang fish in

Khanh Khoa seawater was counted at 149.2 mm (Fig. 5).

Fig. 2 — Histological images of the testes of of the blue tang fish in Khanh Hoa

Spc: spermatocytes; Spm: spermatids; Spz: spermatozoa; Sc: Sertoli cells; L: seminiferous lobule; It: interstitialtissue.

Table 3 — Maturity stages of male blue tang fish in Khanh Hoa

Maturity stages Particular of the gonads

Stage I, Immature Testes was thin, short and glassy in appearance. It could not be distinguished ovary and testes by snake-eyes. The

stages was observed in the fish size under the first maturation size.

Stage II, Maturing Testes start developing, ovary and testes can be distinguished by snake-eyes. Testes are moderately thick,

flattened and white.

Stage III, Mature Testes increase the size comparing to stage II. Testes are flat, well-developed and creamy white, extending about

2/3 body cavity length

Stage IV,

Ripe/Oozing

Testes are very thick, flat, turgid and creamy, extending in the entire body cavity length

Stage V, Spent Testes are sunken


843

The absolute fecundity of the blue tang tang fish in

Khanh Hoa varied from 1.527 – to 20.618

ovaries/individual with an average of 9.983 ± 6.026

ovaries/individual. Relative fecundity of the fish

varied from 28 to 92 with an average of

67 ± 19 ova/gram of females fish. The relationship

between fecundity and the length and weight of fish

was presented as in Fig. 6 and 7.

Discussion

Understanding of the reproductive biology of fish

is necessary for fishery resource management and

aquaculture practices. This is the first attempt to

Fig. 6 — Fecundity - total length relationship of the blue tang fish

in Khanh Hoa

Fig. 7 — Fecundity - total weight relationship of the blue tang fish

in Khanh Hoa

Fig. 3 — Monthly percentages of maturation stages of blue tang fish

Fig. 4 — Monthly change of the GSI of blue tang fish in Khanh Hoa

Fig. 5 — Groups of size relationship and Ln ((1-P) / P) of the blue

tang fish in Khanh Hoa

y = 4.581x - 6.581

R² = 0.935

2.5

3

3.5

4

4.5

5

2.1 2.2 2.3 2.4 2.5

Lo

g F

Log (TL)

y = 1.535x + 0.683

R² = 0.913

2.5

2.7

2.9

3.1

3.3

3.5

3.7

3.9

4.1

4.3

4.5

1.5 2 2.5

Lo

g F

Log BW

0

10

20

30

40

50

60

70

80

90

100Ja

nu

ary

Feb

ruar

y

Mar

ch

Ap

ril

May

Jun

e

July

Au

gu

st

Sep

tem

…

Oct

ob

er

No

vem

ber

Dec

emb

er

Per

cen

tage

(%

)

Month

Stage VStage IVStage IIIStage IIStage I

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Jan

uar

y

Feb

ruar

y

Mar

ch

Ap

ril

May

Jun

e

July

Au

gu

st

Sep

te…

Oct

ob

er

No

ve…

Dec

e…

GS

I %

Month

Male

y = -0.053x + 7.908

R² = 0.922

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

110 130 150 170 190Ln

(1-P

)/P

Length (mm)


844

investigate some reproductive parameters of the blue

tang fish. In this study, the gonad of the blue tang fish

was divided into 5 stages of maturity. This is

normally observed in the tropical fish having the year

round reproduction cycles. At mature or ripe stages,

beside the main component oocytes (oocyte at early

vitellogenic and advanced vitellogenic stage), the

primary growth oocytes also exist at the considerate

number. This is the evidence that blue tang fish

spawn continuously during the spawning season. In

addition, the data on the changes in percentage of

maturity stages and GSI in the current study suggests

that, blue tang fish in Khanh Hoa spawn all year

round with a peak season from April to September.

This results is consistent with others studies on

tropical marine fishes. Fishes in estuary and coastal

seawater all most spawning year round and have one

peak spawning season11&12

. The peak spawning

season of the blue tang fish in Khanh Hoa is similar

to the anemone fish (Amphiprion sp)13

and in

contrast with sliver sillago (Sillaga sihama) (from

December to April)14

. According to Vijay Anand and

Pillai15

the peak spawning season of some species

belonging to family Acanthuridae is different with

the blue tang fish in the current study. Acanthlinis

leucosternon, A. triostegus, Chaetodon collare,

Plectorhinchus orientalis, Parupeneus bifasciatus

have peak spawning season from September to

April, November to May, February to April,

December to May and September to April,

respectively. The different in peak spawning season

and of the different fish species may due to the

species biology and environmental condition.

Fecundity of fishes is usually determined from the

number of ova of the mature group in the ovary. In

the present study, fecundity of Paracanthurus

hepatus, was determined from the examination of

30 specimens. In the present study, fecundity showed

high correlation coefficient with the total length of the

fish. The regression of fecundity and total length can

be expressed as Log F = 4.581*Log (TL) – 6.581 with

R2 value was 0.935. The regression of fecundity and

body weight can be expressed as Log F = 1.535*Log

(BW) + 0.683 with R2 value was 0.913. The absolute

fecundity of blue tang fish in Khanh Hoa seawater is

equivalent to the fecundity of other aquarium fish

such as Chaetodon trifasciatus (1.984-21.975) and

C. melannotris (1.492-24.532)15

. By contrast, this

value is higher than other fish such as Thalassoma

lunare (3.342-10.360); Parupeneus barberinus

(9.234-10.988) Thalassoma hardwicki (4.600-8.743)

và Chaetodon octofasciatus (1.060-2.879)15

; and

lowest than Chaetodon collare (2.763-31.065) and

Parupeneus bifasciatus (2.968-146.373)15

. Similar to

other fish, fecundity of the blue tang fish in the

current study is positive correlated to total length.

This finding suggests that total ovaries in a spawning

season depend on the fish size16

.

Sex ratio of the blue tang fish in the current study was

approximate 1:1. The result is in consistent with other

fish such as Acanthlinis leucosternon15

. However, the

ratio is diffent to others species such as A. triostegus

Chaetodon collare; Plectorhinchus orientalis;

Thalassoma hardwicki15

.

The length at sexual maturity of the blue tang fish

in Khanh Hoa seawater in the current study is larger

than that of two other fish belonging to family

Acanthuridae: Acanthlinis leucosternon (101 -120 cm)

and A. triostegus (71-100 cm)15

. This may due to the

species characteristics and the maximum size as well

as the life cycle of the fishes.

Conclusion The present study reveals that blue tang fish in

Khanh Hoa seawater spawns year round which peak

season from April to September, length at first sexual

maturity of the fish is 149.2 mm. Fecundity ranged

from 1.527 – to 20.618 ovaries/ and strongly related

to weight and length. The currently findings provide

the scientific foundation for the purpose of fishery

resource management and artificial breeding of the

blue tang fish.

Acknowledgments The authors are grateful to Ms. Nguyen Tuong Vy,

Ms. Phan Thi Ngoc for contributing to sample collection

and analysis. This work is finacially supported by

Vietnam Academy of Science and Technology (VAST)

under the project number VAST06.04/15-16.

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