blue barred parrot fish (scarus ghobban forsskal, 1775...
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Indian Journal of Geo Marine Sciences
Vol. 46 (08), August 2017, pp. 1614-1620
Blue barred parrot fish (Scarus ghobban Forsskal, 1775) culture in sea
cages at Rameshwaram Island, Southeast coast of India
Santhanakumar Jayapal, Sendhil Kumar Ramaiyan, Dharani Gopal, Rasheeda Kothalia,
Vijayakumaran Manambarakat & Kirubagaran Ramalingam*
National Institute of Ocean Technology, Pallikaranai, Chennai-600 100, India
*[E-mail: [email protected] ]
Received 07 April 2015 ; revised 22 November 2016
Two square HDPE cages of 2 x 2 x 2.5 m (10 m3) size were deployed at 6 m depth in the sea at a distance of 600 m from the
shore at Olaikuda fishing village. Live parrot fishes of <450 g procured from the trap fishers were sorted out into two size
groups viz. 200-245 g ( 214.00 ± 16.63 g) and 375-450 g ( 425.00 ± 20.64 g) and stocked @ 8.5 kg/m3 separately in these
cages. Low value shrimp head waste was fed @ 8-10% of total biomass stocked. The fishes were reared for two months and the
culture was terminated due to severe blooming of the blue green alga, Lyngbya sp. Average weight gain during this 2 month
culture varied between 44 g (GR 0.73 g/day) in the smaller group (200-245 g) and 98 g (GR 1.61 g/day) in the bigger group
(375-450 g). A second culture trial was conducted with wild caught young fishes of approx. 100 to 140 g size and stocked them
in a 9 m dia circular cage of 320 m3 cultivable volume. Culture was conducted for 130 days with pellet feed and a survival rate
of 95% with the growth rate of 0.61 g/day (total average weight gain of 79.0 g).
[Key words: Parrot fish, Scarus ghobban, trap fishing, sea cages and sea farming.]
Introduction
The blue barred parrot fish Scarus
ghobban is a protogynous fish with fused teeth
and bright colours found in tropical coral reef
environments of Indian, Pacific and Atlantic
Oceans1. The major stomach content analysis of
this fish revealed large quantities of calcareous
powder forecasting its coral grazing behaviour2
causing bio-erosion of tropical reefs3 and is
assumed to be responsible for the coral sand
formation4, 5
. It is estimated that a single fish of
this species can produce up to 90 kg of
sand/year6. S. ghobban is gaining commercial
importance7 owing to increased demand for
human consumption and for its ornamental value.
In the Gulf of Mannar (GoM) on the southeast
coast of India, this species supports a small
fishery and is sold either as fresh in local markets
or exported (0.5 to 1.5 kg) as fillets or whole
frozen mainly to Amsterdam8. Live S. ghobban
attracts good price (US $ 20-40/kg) in
international market9. Randall
10 compiled the
systematics of parrot fishes with an emphasis on
its sexual dimorphism. Earlier studies on parrot
fishes describe their phylogeny, ecology,
demography, food and feeding, length-weight
relationship, life history and bio-erosion
capabilities11, 12, 13, 14
. Varghese15
and Veeramani13
studied the length-weight relationship of S.
ghobban in Indian waters and Sabetian12
studied
the same in South Pacific region. However, no
report is available on the growth of S. ghobban in
sea cages. Scarus ghobban is the dominant reef fish captured
live in considerable quantities between March and
September in GoM area at a depth of 2-12 m by
setting traps made up of synthetic and natural
fibers in the fishing hamlets of Olaikuda, Vada-
kadu, Ariyankundu and Nalupanai in
Rameshwarm Island (9o 17’ 37.26” N; 79
o 19’
31.83” E and 9o 19’ 16.59” N; 79
o 17’ 41.42” E).
The market preference of this fish is directly
related to its size and categorized accordingly into
3 grades as small (<500 g), medium (500 to 1000
g) and premium (>1000 g) with price tags of ₹80,
₹250 and ₹350/kg, respectively. A majority of the
catches are of the smaller size group giving low
return to the fishers. As these fishes are caught
INDIAN J. MAR. SCI., VOL. 46, NO. 08, AUGUST 2017
live, growing the small fish to the next higher
grade of above 500 g would increase its market
value considerably in a short period. No attempt
has yet been made anywhere to grow this fish
commercially and the present study is the
pioneering attempt to explore the possibilities of
rearing small S. ghobban to obtain better market
value and also to assess the potential of this
species prior to considering it as a candidate for
aquaculture. Acclimatization of parrot fish to the
cage environment, stocking density, feeding
behaviour and live fish transport were explored
during the course of this experiment.
Materials and Methods Experimental sea cage culture in
Olaikuda (9o 19’ 9.3” N; 79
o 19’ 44.7” E) was
initiated in 1st week of August 2010 with high
density poly ethylene (HDPE) cages fabricated
and deployed at 6 m depth in the sea about 600 m
away from the shore. The site was selected based
on its comparatively favourable sea conditions for
cage culture such as relatively calm and clear
water, pollution free environment, availability of
young parrot fish seeds and also the enthusiasm
shown by the villagers (Fig. 1).
Fabrication of sea cages and its mooring
configuration
Two types of HDPE cage models such as
square (2 × 2 m2) and circular (9 m dia) were
fabricated and deployed with single and
multipoint mooring systems, respectively, in the
culture site for marine finfish culture trials.
Initially the square cages (2 Nos.) with
dimensions of 2 x 2 m were fabricated with the 25
mm thick and 450 mm outer diameter HDPE
pipes. Two types of nets, a fish holding net with
2.5 cm mesh size (knot to knot) on the inner side
and a predator net with 6 cm mesh was fitted on
the inner and outer sides of the HDPE frame,
respectively. The gap between these two nets was
maintained at 40 cm in all sides of the frame. The
purpose of fish holding net was to accommodate
the fishes to be grown and the predator net was to
prevent the entry of larger fishes and other
predators and also to minimize the clogging
caused by seaweed fouling on the fish holding
net. Suitable ballasts were prepared with 3.81 cm
outer dia polyvinyl chloride pipe with cement
packing to stretch these nets to maintain the
square shape and thereby provide maximum space
to the fishes reared. The square cages were
moored with an appropriate single point mooring
system as indicated in the Fig. 2. A conventional
type circular cage with 9 m diameter was
fabricated and deployed at 8 m depth region with
above mentioned specification as shown in the
Fig. 3.
Fig. 1- Map showing the cage culture site at Olaikuda,
Rameshwaram Island, India
DimensionFish holding net : 2 x 2 x 2.5 mPredator net : 2.5 x 2.5 x 3 m
Depth : 4 m
Fig. 2- Anchoring & mooring configuration of square cage* *Fish holding net: 2.5 cm mesh size and 2 mm thickness;
Predator net: 6 cm mesh size and 3 mm thickness; HDPE
cage frame: 450 mm dia. 25 mm thickness; Galvanized chain
10 mm thickness; Primary anchor: 200 kg; Secondary
anchor: 150 kg; and Polypropylene rope 25 mm thickness.
Live fish transportation
Juvenile parrot fishes were collected from
trap fishermen of Olaikuda village and
transported to the culture cages. Live fish
transportation was standardized after many trials.
Initially the fish were transported in plastic tubs
with battery aerator, during the process the fishes
started secreting large quantities of mucous which
choked the gill rackers and reduced the efficiency
of oxygen exchange rate causing ultimately stress
and mortality of the fishes. Hence, an attempt was
made to use traditional net bag (Fig. 4a) which
can be dragged in water column to the cage site.
This was later improved by adding 2 mm thick
iron rings in the middle of the net bag to give a
non-collapsible shape to the bags (Fig. 4b) which
minimized the skin aberration while transporting
the fishes.
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SANTHANAKUMAR et al.: BLUE BARRED PARROT FISH CULTURE IN SEA CAGES
Fig. 3- a. Circular cage (9 m Ø) and b. its multi-point
mooring used for parrot fish culture at Olaikuda* *Fish holding net = 0.8 cm mesh size and 1.4 mm thickness;
floating HDPE cage frame: 200 mm dia. 8 mm thickness;
galvanized chain 2.5 cm thickness (250 kg; 8 nos.); -
indicating the position of Samson anchor: 250 kg.
Stocking, feeding and cage maintenance
The healthy fishes were initially stocked
in 1 m3 Fiber Reinforced Plastic (FRP) cage for
quarantine/observation purpose. After 24 hrs of
observation, the active fishes were transferred to
grow out cages. Before stocking in the grow out
cages, weight of the fish were recorded and sorted
into 2 size groups as 200-245 g ( 214.00 ± 16.63
g) and 375-450 g ( 425.00 ± 20.64 g) and
stocked separately in two square cages. The fishes
were fed twice a day with low value shrimp head
waste @ 8 – 10% of total biomass stocked. The
shrimp head waste purchased from the nearby
trawl landing centre was selected over low value
feed for the trial as it was found to be preferred by
the parrot fishes during initial feed preference
trials and also owing to its consistent availability.
The fishes stocked during the first week of August
faced an unusual wind and wave action that
caused mass mortality in both the cages during the
first week of stocking itself. The dead fishes had
skin abrasions, reddening of eyes and empty
stomach due to the rough weather which caused
friction with the knotted nets. To reduce the
friction and the subsequent rashes, a polythene
sheet was overlaid at the inner bottom up to 30 cm
height of the fish holding net. The cages were
restocked with new seeds during early morning or
late evening hours to minimize the heat shock to
the fishes. The fish restocked were grown in the
cages for 2 months from August to October. The
unconsumed feed and exoskeletons (carapace
with rostral spines) were removed in the early
hours every day to maintain a clean environment
in the cages. To study the growth and survival of
the parrot fish in caged environment, a second
culture trial was initiated in subsequent year
during the fair weather period of this site i.e. June
to October for the period of 130 days with wild
caught smaller fishes of approx. 100 to 140 g size
and stocked in a 9 m dia circular cage of 320 m3
cultivable volume with the estimated stocking
density of 4 kg/m3. Nets were routinely cleaned to
reduce drag and maintain consistent water flow
through the cages. Daily diving was performed in
both the locations for observation of nets and
removal of dead fishes. Feeding and mortalities
were recorded daily.
Fig. 4 - Types of (a) traditional and (b) modified bags used
for live transportation of S. ghobban
Physicochemical parameters such as
salinity (‰), temperature (⁰C), pH and dissolved
oxygen (DO; mg/L) were measured with YSI
(Model 563A) water quality measuring probe.
Nutrients levels were estimated by following
APHA manual of standard procedures. In order to
estimate the growth rate, 4 nos. of active fishes
from both size groups in square type cages were
pre weighed and tagged. After harvest, the tagged
fishes were separated and measured and the
growth was calculated by deducting the initial
weight (IW) from the final weight (FW) of the
fish. In case of the 9 m dia circular cage, the
fishes were sampled every 15 days to measure wet
weight. The growth rate (GR) was calculated by
Mouth
Iron ring
Mesh (1cm)
Mesh (1cm)
Mouth
Mesh bag (Traditional name – Aracha) Mesh bag with iron ringLength – 45 cm; Width – 35 cm Length – 60 cm; diameter – 35 cm
4a
4b
3a
3b
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INDIAN J. MAR. SCI., VOL. 46, NO. 08, AUGUST 2017
dividing the weight increment (WI) with duration
of the culture (DOC) period and the GR was
expressed as g/day. Filaments attached in the
predator net were collected and preserved in
amber poly bottle containing of 4% buffered
formalin solution to prevent colour loss to easy
identification.
Results and Discussion
The range of water quality parameters
recorded in sea water at the culture site is given in
Table 1. Temperature of the study area varied
between 27.3 and 29.7˚C, which was very close to
the recommended range (25-30˚C)16
for tropical
finfish aquaculture.
A mild salinity variation observed in the
culture site (34.2 and 34.8) was comparable to the
observations17, 18
for the same season at this
location. The pH ranged from 8.00 to 8.27.
During the cage culture period, the dissolved
oxygen was between 2.98 and 5.12 mg/L in
bottom water and 4.7 - 5.96 mg/L in surface
water. Lower level of DO (2.98 mg/L and 3.10
mg/L) was observed in the early hours at 2 am
and 4 am (Fig. 8), respectively, in bottom waters
of 6 m depth, which is comparable with the
observations19
on DO depletion during algal
blooms. Total suspended solids (TSS) levels were
recorded between 8.32 and 38.16 mg/L which are
comparatively higher than the suitable level of
<10 mg/L for cage culture site20
. Higher quantity
of TSS recorded during the month of October was
attributed to the decomposition and disintegration
of dead algal cells (Lyngbya sp). The nutrients
levels such as ammonia (0.02 - 0.37 mg/L), nitrite
(0.11 - 0.91 mg/L) and nitrate (3.11 - 12.40 mg/L)
recorded at this site were comparable to the
previous studies17
in Palk Bay and within the
optimal range suggested for fish farm20
.
The seaweed (Kappaphycus alvarezii)
also was being cultured in floating wooden rafts
adjacent to the fish cages by local fishermen.
Filamentous algal growth was observed on the sea
weed culture rafts in August 2010. The algal
growth progressed to heavy bloom in September
and created many problems for the sea weed
culture. Thick blooms of the algae surrounded the
seaweeds, preventing its growth and ultimately
leading to its death and putrification. Settling of
algal filaments was observed up to a height of 2
feet at the bottom and covering the anchors and
mooring chain in and around cage culture site.
The thick growth of algae also completely
covered the mouth of fish traps placed at 4-5 m
depth and the fish cage was not spared as the nets
were severely clogged (Fig. 5, 6 and 7).
Live transportation of S. ghobban from
the fishing ground to the cage site was
standardized after many trials. In the first method,
where the fish were kept in tub containing aerated
water with battery aerator, 90% of the fish died
due to gill chocking caused by excess mucus
released by them. Another attempt was made to
transport these live fishes by net bags used for
dead fish collection which was dragged to the
cage site in immersed condition in sea water at a
speed of 1.5 knot / hr. It resulted in the reduction
of mortality up to 50% but the dead and live fish
had injuries such as scale loss, abrasion in skin
and reddening of the snout region. Though the
second method provided good water circulation to
the fishes, the shrinking nature of the bags when
dragged caused injuries leading to subsequent
mortality. To overcome the shrinking of net while
dragging and to maintain a definite circular shape
to provide sufficient place for the fish two circular
iron rings (2 mm thickness) were introduced (Fig.
3). The modified fish transporting bag improved
the survival of the fishes up to 90% during
transportation.
Underwater observations revealed that the
fish preferred to stay at the bottom of the cages
and during windy periods the cage frames were
Table 1: Range of water quality parameters at the experimental culture site during the study
Water
Temp.
(˚C)
pH Salinity
(‰)
DO
(mg/L)
TSS
(mg/L)
NO2
(mg/L)
NO3
(mg/L)
NH3-N
(µmol/L)
Range 27.30-
29.70
8.00-
8.27
34.20-
34.80
2.98-
5.96
8.32-
38.16
0.11-
0.91
3.11-
12.40
0.02-
0.37
Mean ( ) 28.40
±0.71
8.18
±0.07
34.40
±0.21
4.29
±0.93
20.58
±10.03
0.51
±0.27
3.93
±2.55
0.20
±0.12
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SANTHANAKUMAR et al.: BLUE BARRED PARROT FISH CULTURE IN SEA CAGES
lifted frequently by waves which lead to sudden
jolting to the culture system causing injuries to the
fish. This unexpected event of rough weather
caused mass mortality of fish in the first week of
stocking owing to the fish hitting the knots in the
nets and getting injured. Such a problem was also
reported for other cage grown fishes in knotted
net bags 21
. The dead fish had signs of tail rot, fin
rot, snout injuries and reddening of skin. When a
polythene sheet was overlaid on the inner bottom
of the fish holding net there was considerable
recovery of injured fish. The cages were then
hauled close to the shore where much protected
areas were available to reduce adverse effect of
waves on the cages. The above decision was made
based on the observation on the quarantine cage
(1 m3) deployed in the near shore region where
the fishes were safe and comfortable during the
same turbulent weather. After this intervention,
the mortality of fishes was brought to a halt.
Scarus ghobban is reported as a primary
consumer feeding on sea grass14
and benthic algae
associated with corals and stones2, 22
. It was
observed in the present study that it prefers to
feed on crustaceans such as shrimps and crabs as
well in captive condition. Hence, during the
culture, shrimp head waste, a low cost by product
from shrimp processing units, was used as feed.
Fishers in the locality use crustacean waste as bait
to capture the fish by traps. These bottom
dwelling fishes will wait for the feed to come to
the mid column water before coming up to
consume it. Due to this nature, sufficient quantity
of sea sand was mixed with the feed (shrimp head
waste) to enable it to sink. Fishes reared in 9 m Ø
sea cages (smallest weight group) were however
fed with commercial slow sinking pellets (Brand:
Lucky star; size: 3-5mm) prepared for sea bass.
Fig. 5 - Growth of filamentous alga (Lyngbya sp.) on fish
cage nets (a) and its view under microscope (b)
Fig. 6 - Filamentous algal settlement covering fish traps
operated (2 days) at the site
Fig. 7- Arrows indicating the dead polychaetes along with the
shored filamentous alga
Fig. 8 - Patterns of surface and bottom DO levels during the
algal bloom
The results obtained after 2 months
rearing of S. ghobban, such as GR, mean final
body weight and final biomass of different size
groups (200-245 g and 375-450 g) are given in
table-2. The stocking density of 8.5 kg/m3 can be
further improved as the fishes are domicile in
0
1
2
3
4
5
6
7
DO
lev
el i
n m
g/L
Surface
Bottom
Microscopic view
100 μ
5a
5b
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INDIAN J. MAR. SCI., VOL. 46, NO. 08, AUGUST 2017
nature without much aggression in the cage
environment. Increment in the average weight of
the fish was considerably higher (98 g, GR 1.61
g/day) in the bigger fishes and less (44 g, GR 0.73
g/day) in smaller fishes. Growth rate of the S.
ghobban is comparable with other commercial
fish species such as Snappers (1.82 g/day in the
110 g size group) and groupers16
.
Table 2: Summary of growth parameter estimates of S.
ghobban from square and circular cages
Parameters 100 – 140 200 – 245 375 – 450
Mean initial weight (g) 125.00 ±
9.40
214.00 ±
16.63
425 .00±
20.64
Mean final weight (g) 204.00
± 27.82
252.00 ±
11.62
523.00 ±
20.32
Days of culture (d) 130 60 60
Avg. wt. increment 79 44 98
Initial biomass (kg) 162.5 85.23 85.16
Final Biomass (kg) 251.9 59.28 66.49
Average GR (g/day) 0.61 0.73 1.61
Survival (%) 95 59 63
The smaller parrot fish cultured in 9m Ø sea cages with pellet feeding (Lucky star-sea bass feed; size: 3-5mm) for a period of 130 days, had a survival rate of 95 % with of 0.61 g/day increase in growth rate and the overall weight gain of 79g (Fig. 9 &10).
Fig. 9- Growth rate in parrot fish of two weight groups (200-
245 g and 375-450 g)
Though the weight gain in pellet fed fish was
lower compared to the ones grown with shrimp
head waste, it is encouraging to demonstrate that
parrot fishes can be grown on pellet feed. A
dedicated feed needs to be formulated to meet the
nutritional requirement of this species to get better
growth rate.
Fig. 10 - Growth performance of fishes stocked in 9m dia
Conclusion
The results of the present study reveals
that parrot fishes can be grown in the sea cages
like any other fishes presently being used for sea
farming. These fishes can be acclimatized to the
cage culture system and fed with crustacean
wastes or with formulated pellet feed for growing
them for a shorter duration of 2 to 3 months for
value addition. Since these fishes prefer to live at
the bottom, the depth of the cage needs to be a
minimum of 2 to 3 meters. While feeding the
fishes, it should be ensured that the feed sinks to
the bottom of the cages since the fish prefer to
wait for the feed to sink to the middle of the water
column to feed. The effect of rearing these fishes
in a cage environment for a longer duration needs
to be studied to know the nutritional requirement
and suitable density for culture. In the absence of
hatchery produced seeds, the potential of the
sustainable wild parrot fish seed collection needs
to be assessed prior to initiating a community
level mariculture programme. As fishermen
stated, blooming of filamentous alga in this region
was a new phenomenon, however, the blooming
caused major damages to the sea weed culture and
local fishery. Therefore, periodical observation on
occurrence of the bloom is highly essential to
practice successful sea cage culture of parrot fish
in this region.
Two groups of fishermen comprising 4
members in each group were involved in cage
culture of parrot fishes during their fishing season.
Since, there is no commercial feed available to get
better growth, the fishermen always depend on
shrimp head waste as feed, which is not available
in all the seasons. Hence, the fishermen expressed
their requirement on formulation of suitable feed
is highly essential to get better growth to continue
this culture for all the seasons.
0.0
0.5
1.0
1.5
2.0
200 210 240 245 375 425 445 450
GR
(g
\d)
Fish weight groups in g
100
120
140
160
180
200
220
240
0 15 30 45 60 75 90 105 120 130
Culture period in days
Wei
gh
t in
g
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SANTHANAKUMAR et al.: BLUE BARRED PARROT FISH CULTURE IN SEA CAGES
Acknowledgements
Authors gratefully acknowledge the
financial support given by the Earth System
Sciences Organization (ESSO), Ministry of Earth
Sciences, Government of India. Authors are
thankful to Dr. S. S. C. Shenoi, Director, ESSO-
National Institute of Ocean Technology, Ministry
of Earth Sciences, Government of India, for
constant suggestions and encouragements.
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