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: kiruba@niot.res.in ]

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

1616

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

1617

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

1618

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

1619

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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