Grouper Culture and
A Review of the Grouper Breeding Programme in
Singapore
T.
M. Chao and R. Chou[1]
Abstract
There are 84 commercial
floating fish farms in Singapore, located in the coastal waters of the East and
West Johor Straits. These farms are responsible for 3,554 tonnes of aquaculture
products valued at S$13.5 million (US$9.6 million) in 1995. Mainly estuarine (Epinephelus tauvina),
brown-marbled (Epinephelus fuscoguttatus) and malabar (Epinephelus
malabaricus) groupers are among the more popular marine food fish cultured.
Grouper species consists of 12.5-3.3% of total production tonnage and 31-19.9%
of the total value for 1991 to 1995. The reductions in production of grouper
over the years have been possibly due to the decrease in supply of fry and
fingerlings from the wild. The emergence of seabass as the good alternative for
restaurant fish could be another reason contributing to a decline in grouper
production. This paper describes how grouper is commercially farmed in
Singapore and the research efforts made with grouper species, initiated since
1971, which has made incremental progress in broodstock management and
larviculture zootechniques. The recent major achievement from a three-year
grouper breeding programme between Primary Production Department and National
University of Singapore and sponsored by the National Science and Technology
Board was the isolation and purification of gonadotropins and growth hormone
from estuarine grouper pituitaries. Mass cloning of these purified hormones is expected.
It is envisaged that the application of these cloned hormones in near future
would improve the spawning performance and eventually larval survival of
estuarine grouper.
Introduction
Singapore, an island state
with a territory covering 646.1 km2 and a population of 2.98 million
people, is situated approximately 136.8 kilometres north of the equator. It is
in the centre of Malayan Archipelago and at the crossroads of the Pacific and
Indian Oceans. Due to the scarcity of land, the focus on agriculture is on the
development of intensive farming systems and at maximising production and
economic returns per unit area or effort. The farming of marine food fish in
floating net-cages was identified in early 1970s as a suitable intensive
farming system to supply fresh and live fish in Singapore.
The Primary Production
Department (PPD) initiated research on marine fish aquaculture in Singapore in
1971. Since then, several marine food fish species were studied with the aim of
achieving constant and sufficient seed supply for the marine fish aquaculture
industry. The species studied are:
estuarine grouper or greasy grouper, Epinephelus tauvina or Epinephelus
coioides; polkadot grouper, Cromileptes altivelis; seabass, Lates
calcarifer; golden snapper, Lutjanus johnii; brown-marbled grouper, Epinephelus
fuscoguttatus; the mangrove red snapper, Lutjanus argentimaculatus;
and four-finger threadfin, Eleutheronema tetradactylum (Chen et al., 1977; Lim et al., 1986; Lim et al., 1985; Lim et al., 1990; Lim and Chao, 1993; Chao et al., 1994). This paper will address
the culture of grouper and research and development efforts on its breeding in
Singapore.
Commercial Net-cage Grouper Farming
The Marine Fish Farming
Scheme was introduced by PPD in March 1981. Since then, the marine fish
aquaculture industry in Singapore has grown from 32 to 84 licensed net-cage
fish farms in 1995. The annual marine aquaculture production has increased from
2,191 tonnes in 1991 to 3,554 tonnes in 1995 (Annex 1). In 1995, these 84 net-cage
fish farms occupying 46.5 ha of the coastal area in the Johor Straits (Annex
2), produced 3,554 tonnes, valued at S$ 13.5 million (US$ 9.6 million, at US$
1.00 = S$1.40). This accounted for
about 98% of the total aquaculture production of 3,625 tonnes. The 5-year
marine aquaculture production is shown in Annex 2. Grouper species consists of
12.5-3.3% of the total production tonnage and 31-19.9% of the total value over
the 5-year period. Although the total annual production and value of grouper in
relation to the overall farm's production have declined over the years, the
ex-farm price of grouper is still quite stable (at S$20-22 per kg or US$
14.3-15.7 per kg). The decrease in the seed supply of grouper could be the main
reason for the production decline. The emergence of seabass as the good
alternative for restaurant fish in Singapore could be the other reason.
Species of Groupers Farmed
in Net-cage Farm
The estuarine grouper is the
main species of grouper farmed in floating net-cages. Other minor grouperspecies
are brown-marbled grouper, malabar groupers (Epinephelus malabaricus),
the coral trouts (Plectropomus maculatus and P. leopardus) and
polkadot grouper (Cromileptes altivelis).
The groupers are selected
for their high market value, especially when sold live to the market. The other
important criteria for farming grouper are: tolerance to high stocking
densities at 16 fish/m3 or 40 fish/m2; expectation of
yields of about 16 kg/m3 or 24 kg/m2; fast growth (6-8
months per cycle); and availability of seed supply, albeit seasonal.
Farm Design
The basic farm design for
marine food fish, introduced by PPD in the 1970s, is suitable for grouper
culture. The design consists of a net-cage proper and a wooden raft from which
the net-cages are suspended. The wooden raft is made up of wooden beams,
assembled into lattices and kept afloat by about 350-400 plastic drums, each of
250-300 litre capacity. Polyethylene net-cages varying from 2x2x2m (deep) to
5x5x3m (deep, 8-50 mm in mesh size) are suspended from the frames. Net-cages
are generally classified according to mesh sizes: hapa (8 mm mesh size,
knotless nylon), nursery (25 mm mesh size, polyethylene) and production (50 mm
mesh size, polyethylene). Adjacent to the floating frame is a wooden work hut
and platform for feed preparation and storage of equipment and materials. The
farm (frames and hut) occupies about 1,500-2,000 m2 (about 30-40%)
of the half hectare (5,000 m2) of sea space that PPD leases out to
the farmer at S$650 (US$464) per year. The present fish farms still generally
follow this design as shown in Annex 3.
Farming Methodology
The grouper farming method
is quite straightforward with a somewhat fixed sequence of events per culture
cycle (Anon., 1986). Grouper fingerlings, 75-100 mm in total length obtained
either from natural catches locally or more usually imported, are stocked
initially at 100-500 fish/m2 of net bottom area into hapa
nets. The grouper fingerlings are usually held in the hapa for a month
or so until they attain 125-150 mm in total length, when they would be thinned
out to nursery nets at about 44 fish/m2. Subsequently, after 2-3
months they are transferred to production net and grown until market-size of
600 to 700-g body weight when they are harvested. At the time of harvesting,
that is 6 to 8 months from stocking in the nursery net, groupers would have
thinned themselves out naturally, with a natural mortality of 5-10% to about 40
fish/m2. By manipulating the management of stocking and feeding, a
farmer can have a continuous batch of fish produced throughout the year.
Net-cage farmers still
prefer to use trash fish as feed for grouper (Chou and Lee, in press). Trash
fish is the by-catch of trawlers, comprising small fish of low economic value
(S$500/tonne or US$357/tonne), like goatfish (Upeneus spp.) and
jewfish/croakers (Pennahia spp.). Trash fish is chopped to smaller
pieces before being fed to fish in the net-cages. Feeding rate is 10% body
weight during the hapa stage, reduced to 8% body weight at the nursery
stage and finally 5-3% during the grow-out stage. It is estimated that feed
conversion ratio for grouper is 4.5:1. In some farms, semi-moist feed is
prepared on-farm for groupers and other fishes, usually when bad weather limits
the availability of trash fish from trawlers. The formulation for semi-moist
feed is simple, comprising fishmeal (30%), corn gluten (70%) and vitamins and
minerals (0.5-1%). Alternatively, the farmer will mix ground trash fish
(30-50%) with a binder mix consisting of fishmeal, soya bean meal, rich bran,
corn gluten or wheat flour, vitamins and minerals. The mixture is either hand
or machine mixed with hot water to gelatinise the starch (Chou, 1995).
Harvesting of groupers is
done manually by two farm workers. They lift the net-cage and gather the
groupers and scoop them out into waiting transport tanks in boats that take
them to shore for direct transfer to lorries and then to restaurants.
Disease Control
Disease of grouper species
may arise for various reasons for example stress, parasites, pathogens and
nutritional imbalance. Importation and handling mortalities are two instances
where stress is directly involved. To control post-importation mortalities,
farmers are advised to carry out sanitation by special arrangement with the
fish fingerling agent in the country of origin, or the farmers themselves can
perform it. Comprehensive sanitation protocols that includes pre-shipment,
trans-shipment and on-farm sanitation are recommended to fish farmers for
improving the health status of imported fish fingerlings (Chong and Chao, 1986;
Khinet et al., 1987).
Pre-shipment sanitation requires the fish fingerling agent to treat the grouper
with acriflavine (10 ppm) prior to dispatch. Trans-shipment sanitation involves
the addition of 10 ppm of nitrofurazone to fish transport water. On-farm
sanitation comprises a 100 ppm formalin bath of 1 hour, followed by a
nitrofurazone (30 ppm) for 4 hours. Antibiotic prophylaxis, for example
oxytetracycline at 0.5g/kg feed daily for 7 days, may further increase survival
of sanitised fish, but itself is not as effective as chemical sanitation.
Protozoal diseases like
cryptocaryoniasis caused by Cryptocaryon irritans commonly occurred in
the hapa and nursery stages with groupers. Estuarine grouper displays the classical ‘white spots’. In certain cases, for example, with
re-infestations or secondary involvement with bacteria, open ulcers are formed.
Other protozoal disease agents occurring in groupers are Trichodina sp.
and Brooklynella sp. Due to
difficulty in eradication of Cryptocaryon irritans, besides using
chemical treatment, the farmers are advised to isolate sick fish and remove
dead or terminally sick ones from net-cages and destroy them for the better
control of cryptocaryoniasis on farms. The usual chemical treatment for
protozoal disease is formalin (25 ppm) plus malachite green (0.15 ppm) for 12
hours. Freshwater treatment for one
hour may also help to combat the disease.
Other than protozoal disease, generalised ectoparasitic infestation by
flatworms may occur, for example, Diplectanium sp. and Benedenia
sp. The latter is not an indigenous
species, as there was no occurrence of this ectoparasite before the late 1980s.
Bacterial disease involves
mainly vibriosis in grouper and can be controlled by oral administration of
oxytetracycline (0.5g per kg feed) for 7 days. If the groupers are off feed,
bath treatment of nitrofurazone (15 ppm) for at least 4 hours can be applied.
In general, vibriosis is secondary in nature, occurring as a sequel to trauma
or primary infection by protozoa. However, vibriosis probably accounts for a
significant proportion of importation and handling mortalities. The two
principal Vibrio species, V. alginolyticus and V.
parahaemolyticus and several related strains have been isolated aseptically
from sick groupers. None of them have been consistently identified with
‘vibriosis’, and artificial transmission of the disease, by injection into
healthy fish, requires very high doses of bacteria.
Chong and Chao (1986) first
described swim bladder syndrome in grouper as a fish disease of unknown
aetiology. Chua et al. (1993)
reported the similar occurrence with CPE agent isolated from two outbreaks of
the disease among grouper net-cage farms. A possible viral agent affecting the
central nervous system was implicated. A novel disease occurring in estuarine
grouper, called ‘sleepy grouper disease’ (SGD) was described by Chua et al. (1994). The aetiological agent of
SGD was provisionally identified as an iridovirus and probably introduced with
imported groupers. Until a serological kit for early detection of carriers
among the introduced grouper fingerlings is available, these diseases could
only be controlled by isolation and removal of diseased fish or even a total
eradication of the stock.
An RNA reovirus was isolated
from spleen of coral trout (Plectropomus maculatus) with clinical sign
of inappetence and lethargy, followed by death 2-3 days later. (Chew-Lim et al., 1992). The controlling measure is
the same as other viral diseases.
Varied degrees of lipidosis
are observed in the livers of net-cage cultured groupers. This is a common
nutritional disease among cultured food fish. It is thought that this
phenomenon is linked to rancidity due to poor storage of trash fish and/or the
use of trash fish with high fat content.
Review of
Grouper Breeding Research in Singapore
Histological Study on Gonads of Wild Estuarine
Grouper
Estuarine grouper is
commercially one of the most important fish species and is a highly esteemed
food fish in Singapore and Southeast Asia. Due to its economic value, the
Coastal Aquaculture Unit of PPD initiated production study experiments on this
grouper species in floating net-cages in 1971. However, the supply of
fingerlings from the wild is limited and uncertain and the breeding biology of
the fish was then investigated with the aim of mass-producing them under
controlled conditions. Tan and Tan (1974) demonstrated that the grouper is a
protogynous hermaphrodite through gonadal histological studies. They showed the
biological minimum size of the grouper was 450-500 mm and that male fish had
testes at around 740 mm in standard body length and more than 11 kg in body
weight. Transitional gonads containing male and female gonadal tissues occurred
in fish of 660-720 mm.
Breakthrough in Induced Spawning and Larviculture
Chen et al. (1977)
reported on the breakthrough success of the induced breeding. Accelerating sex
reversal of 3-year old females through hormonal manipulation mainly attributed
it. The broodstock matured as females at the age of 2 years and at 412-500 mm
in standard length. Administrating human chorionic gonadotropin at a dosage of
500-1000 IU (International Units) effected induced ovulation per kilogram of
recipient fish. More effective results were obtained when extracts of pituitary
glands of either white snapper or chum salmon were given in the final
injection. The larval development and its feeding protocol were also described.
Chen (1979) reviewed progress and problems in grouper culture. The large-scale
grouper production was hampered by shortage of fingerlings and feeds (trash
fish) in nursery stage, the inappropriate size of larval food organisms in the
larviculture stage and cannibalism during metamorphosis and juvenile stages.
Chao and Chow (1990) further reported the effect of methyltestosterone on
estuarine grouper gonadal development. The technique to produce maleness in
grouper by oral administration of 17a-methyltestosterone at a
dosage of 1-2 mg/kg body weight at twice or three times a week was established
and documented.
Development in Broodstock and Larviculture
Chao and Lim (1991) reviewed
the problems and progress in the development of grouper breeding technology.
The major problems were the supply of good quality eggs for larviculture and
high mortality during critical periods in the larval stages. Several new
techniques were also reported. These included a hormone implantation technique
for inducing sex reversal in estuarine grouper and a natural spawning technique
for brown-marbled grouper. The implantation technique could replace the former
method of oral administration of the hormone capsule. A 2-mg liquid silastic
capsule inserted into the abdominal cavity via an implanter is effective in
transforming a mature female grouper of average 3-4 kg body weight to a
functional male.
Enrichment techniques to
broodstock diets and live larval food with highly unsaturated fatty acids (w3-HUFA) to improve egg quality and larval
survival were introduced from Belgium.
Dhert et al. (1991)
reported the broodstock diet enrichment technique that a commercial highly
unsaturated fatty acids booster MARILA (Artemia System, N.V., Gent, Belgium)
was injected into the abdomen of trash fish for feeding to grouper brooders at
a dosage of 50 mg/kg of body weight at thrice a week. This resulted in 21% increase of total lipid content of estuarine
grouper eggs with % increase of the size of oil globule. This improved the
larval survival by 5%. Following the same principles, enriched rotifers and Artemia
nauplii, boosted with a commercial lipid emulsion (SELCO, Artemia System
NV, Baasrode, Belgium) were used to feed grouper larvae. It was found that the grouper larvae fed
with these enriched larval live feeds could withstand the stress tests better
than those fed on normal larval feeds.
The use of super-small (SS)
rotifer as the first food and a refined zootechniques like addition of green
algal water, covering of larval tank, water exchange by through-flowing and oil
removal by triangular oil skimmers to overcome early mortality of the larvae
have also been established (Chao and Lim, 1991 and Lim, 1993). With these
advances in techniques, there were incremental improvements on the larval
survival in various stages of larviculture. However, the overall larval
survival of grouper was still very low (below 1%) and inconsistent.
Brown-marbled Grouper Versus Estuarine Grouper
Unlike estuarine grouper as
described above, the brown-marbled grouper can spawn naturally in net-cages
during the monthly lunar period from the last-quarter moon to just before the
new moon (Lim et al., 1990, Chao
et al., 1993). Lim (1993)
compared the spawning and characteristics of the estuarine grouper and
brown-marbled grouper. It was concluded that the brown-marbled was considered a
better potential species than the estuarine grouper for large-scale production.
The superior qualities of brown-marbled grouper for larviculture are: (i) the
occurrence of natural spawning in net-cages;
(ii) higher egg production and all year round spawning capability; (iii)
higher fertilisation rate and higher percentage in buoyant eggs; (iv) faster
larval development and higher larval survival (Lim et al., 1990, Chao et al., 1993). However, the larval
survival of brown-marbled grouper is also not consistent and well below 10%, which
is not a level for commercial application. We should not ignore the potential
of brown-marbled grouper based on the fact that the egg quality and larval
survival are more superior and higher than that of the estuarine grouper. These
qualities are definitely advantages for future commercialisation.
PPD-NUS
Grouper Breeding Project Phase I (3 Years)
In order to look further
into the problems of poor egg quality and larval survival in grouper, a
three-year collaborative project between PPD and the National University of
Singapore (NUS) funded by National Science and Technology Board of Singapore
was initiated in 1992. The long-term objective of the project was to establish
commercially applicable grouper breeding technology. However, the objective of
the project from 1992-1995 was to look into basic aspects of grouper
reproductive physiology at molecular and hormonal levels.
Studies on Sex-change and Pituitary and Gonadal
Hormones
The sex reversal of the fish
was further studied at molecular level by analysing in vitro metabolism
of gonadal tissues. The steroidogenic potential of the gonadal tissue was also
examined by in vitro metabolism before and after sex inversion with 17a-methyltestosterone (Lee et al., 1995). It was found that 5b-androstane-3b, 17b-diol and 5b-dihydrotestosterone are the
only metabolites in the female phase. Although the production of these 5b-reduced androgens persisted in the male
phase, there is a shift toward the production of 11b-hydroxytestosterone and 11-ketotestosterone
as major metabolites. It was also found that the sperms from the induced males
possess the enzyme, 20a-hydroxysteroid
dehydrogenase (20a-HSD) and their single major
metabolite 17, 20a-P (17a, 20a-dihydroxy-4-pregnen-3-one)
may play a role in grouper reproduction (Tan et al., 1995).
Several new products were
also obtained from the extraction and purification work on grouper pituitaries
by the NUS. They were purified grouper growth hormone, prolactin and GtHa and GtHIIb gonadotropin subunits. The
cloning of these hormones was also performed and achieved.
Studies on Application of Thyroid Hormone and
Cortisol
The other significant
outcome from the project is the development of hatchery techniques of thyroid
hormone treatment. It was first found that the thyroid hormone levels are
higher in buoyant than in non-buoyant estuarine grouper eggs (Lam et al., 1994). However, the evidence only
points to a relationship between the buoyancy and viability of the grouper eggs
and levels of thyroid hormone. It is not clear whether the thyroid hormones are
the cause or the effect of egg buoyancy and viability (Lam et al., 1994). However, the developmental
effects of thyroid hormones on fish larvae have been extensively documented
(Lam, 1994). Therefore, it is of interest that the effect of the thyroid
hormone in grouper larvae and treatment protocols were then studied for
hatchery application. The treatment protocols developed include immersion of
fertilised eggs and oral route via bioencapsulation in Artemia nauplii
to fish larvae (Tay et al.,
1994). The immersion of thyroid hormone solution of fertilised eggs (at 0.5 ppm
triiodothyronine, T3 for 12 hours' post-fertilisation) improved larval survival
and hatching rate. The acceleration of metamorphosis by bioencapsulation
through Artemia nauplii (immersion dosage 0.5 ppm T3 for 6 hours) was
also significant (98% vs 2% metamorphosis rate at Day 35). The synergistic
effect of T3 and cortisol to grouper larvae were also studied (Tay et al., 1997). Clearly, T3 promoted
embryonic development while the role of cortisol remains unclear; both hormones
promoted larval survival and synergism was evident.
Conclusion
Although farming technology
of grouper in net-cages have been well developed and established the
development of grouper breeding technology still continues in Singapore, as
well as elsewhere in the region. In the context of Singapore’s emphasis on high
technology farming, it is still important to establish breeding technology for
this difficult marine food fish. The results from the grouper breeding
programme with the National University of Singapore have been encouraging in
that there is the possibility of using mass cloned hormones to improve spawning
performance; the grouper male hormones identified as responsible for sex inversion
and spermiation could be mass-produced for field application; and the refined
larviculture techniques using thyroid hormone and cortisol could be
incorporated into future hatchery protocols.
Acknowledgment
The authors wish to thank Mr Leslie Cheong, Professor
Lam Toong Jin, and Associate Professor Tan Cheong Huat for reviewing the
manuscript and Mr Hassanai Kongkeo, Coordinator of the Network of Aquaculture
Centres in Asia-Pacific (NACA) for the invitation to present this paper.
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thyroid hormone on metamorphosis in greasy grouper, Epinephelus tauvina. Singapore
J. Pri. Ind. 22 (1): 35-38.
Tay, H. C., A.
N. Yong, T. M. Chao, J. Goh, H. S. Lim, R. Chou and T. J. Lam. 1997. Effects of
treatment of eggs with triiodothyronine and cortisol on the morphometry of
newly hatched larvae and larval survival in the greasy grouper (Epinephelus
coiodes). Aqua. Int. 5:189-195.
Annex
1
WEIGHT AND VALUE OF MARINE AQUACULTURE PRODUCTION IN
SINGAPORE (1991-1995)
(with
special reference to grouper production in relation to total production) (in
weight, W: metric tonnes, and in value, V: million S$)
|
Year |
1991 |
1992 |
1993 |
1994 |
1995 |
|||||
|
Production |
W |
V |
W |
V |
W |
V |
W |
V |
W |
V |
|
Finfish Seabass Grouper Snapper Others |
331 274 116 101 |
2.55 5.73 1.00 1.64 |
393 233 93 67 |
2.91 5.16 1.03 0.96 |
257 166 104 80 |
1.94 4.32 0.89 2.33 |
240 157 62 106 |
2.68 3.9 0.57 1.3 |
285 118 42 199 |
2.94 2.78 0.34 1.39 |
|
Shellfish Lobster Shrimp Crab Mussel |
47 76 272 974 |
2.66 1.59 2.6 0.7 |
41 57 284 1182 |
1.35 1.24 2.36 0.5 |
36 87 470 1462 |
1.25 1.56 3.65 0.57 |
19 16 425 1797 |
.05 0.34 3.04 0.79 |
51 12 342 2505 |
1.83 0.23 3.55 0.91 |
|
Total |
2191 |
18.4 |
2350 |
15.1 |
2662 |
16.5 |
2822 |
13.1 |
3554 |
14.0 |
|
Grouper/ Total(%) |
12.5 |
31.0 |
9.9 |
33.3 |
6.2 |
26.2 |
5.6 |
29.7 |
3.3 |
19.9 |
Source: PPD’s submission for FAO Aquaculture
Production Statistics
Annex 2
LOCATION
OF COMMERCIAL MARINE FISH FARMS IN SINGAPORE
