Larval Rearing tanks - Central Institute of Brackishwater Aquaculture

HAND BOOK OF SEED PRODUCTION AND CULTUREOF ASIAN SEABASS, LATES CALCARIFER (BLOCH)A.R. Thirunavukkarasu, Mathew Abraham and M. KailasarnBullctin No. 18February 2004CENTRAL INSTITUTE OF BRACKISHWATERAQUACULTURE(Indian council of Agricultural Research)75, Santhome High Road, Raja Annarnalaipurarn,Chennai - 600 028.

PREFACEThe euryhaline Asian Seabass (Lates colcarifer) is an important candidatefish species for culture in ponds and cages in freshwater and brackishwater areas.In brackishwater aquaculture, seabass can be considered as a highly potentialspecies for crop rotation and it can also be included as a complementary speciesfor shrimp for the sustainability of coastal aquaculture. Though less in valuecompared to shrimps, seabass can contribute greatly to the production with its easymanagement and less risk in the farming. Seabass farming is extensively practicedin South East Asian countries likeThailand, Malaysia, Singapore and also in Australia,however culture of seabass is largely restricted to the coastal brackishwater pondsin India. The maior constraint in the large scale development of seabass culture isthe non-availability of quality seed in adequate quantity.During the post-disease scenario of shrimp aquaculture, when the sectorwos on the look out for other species for diversification for its sustainobility, theCentral lnstitute of Brackishwater Aquaculture (CIBA), Chennoi has developed acost effective indigenous technology for seabass seed production under controlledconditions. This technology has already been commercialized. CIBA has already~nitiated culture of seabass in different agro-climatic regions of the country andencouraging results on growth and production are achieved.The Institute isdeveloping suitable formulated feed for the culture of seabass~nd it is under fieldtrials now.It is hoped that these advancements will pave the way forlarge-scale adoption and culture of seabass in both the coastal regions of thecountry, in the years to come. I hope this bulletin will be useful as a practical guideto fish farmers, entrepreneurs, planners and students of aquaculture.Chennai - 2818-2-2004Mathew AbrahamDirector

CONTENTSPage No.1. Introduction7. Biology of seabass703. Controlled breeding under captive conditions1:4. Larval rearing5. Nursery rearing6. Packing and transport of seed7. Culture8. Harvesting and marketing of seabass207 7451057

1. INTRODUCTIONAquaculture, with a potential for rapid and continuous growth, is one of themain food production activities that can meet the nutritional security requirementsof the people. With an annual growth rate of 1.4%, aquaculture also offers scopefor employment opportunities, especially for the rural folk. The aquaculture resourcesof India are vcst and varied. The country is bestowed with 81 29 km of coastline,0.5 million km2 of continental shelf, 2.02 million kml of exclusive economic zone,3.15 million ha of reservoirs, 2.25 million ha of tanks and ponds, 0.82 million haof beels, oxbow lakes and derelict water bodies and 1.19 million ha of brackishwaterareas. Added to these, around 8 million ha salt affected soils ore spread overinland and coastal states where the available surface and ground water are neithersuitable for ogriculture nor for drinking purposes, but can be productively used forsalt - water fish culture.Presently aquaculture contributes to 80% of the inland fish production. Thefreshwater aquaculture is mainly contributed by the Indian maior carps and thebrackishwater aquaculture by tiger shrimp Penoeus monodon. However, theaquaculture sector is facing challenges in recent years. While freshwater aquacultureis facing problems like low market price for the fish produced, shrimp aquacultureis passing through a critical phase due to the recurring outbreak of White SpotSyndrome Virus (WSSV) disease along with sociol and environmental issues. Toovercome these difficulties, the freshwater aquaculture sector needs value addedfish species that can fetch high unit price and the brackishwater sector has to adoptmore eco-friendly aquaculture practices with species diversification and crop rotation.The Asian seabass, lates calcarifer also known as 'Giant perch', 'Cock - up'or 'Bhetki', which supports the fishery in the Indo-Pacific region in the nearshorewaters, estuaries and inland waters is considered as a candidate species fordiversification in aquaculture. Seabass contributes around 20,066 metric tonnesannually to the total world aquaculture production of 3.6 million tonnes. The Asianseabass is a fast growing, euryhaline fish capable of withstanding wide environmentalfluctuations and can be cultured in ponds ond cages in marine, brackishwater andfreshwater eco-systemsIt is estimated that around 20-30% of the shrimp ponds are not in use becauseof the uncertainity and fear of loosing the crop due to diseases. If 50% of theseunutilized ponds are used for seabass culture, even at a conservative productionrate of 4t/ha, 60,000 tonnes of fish can be produced. Seabass can be cultured in

floating net cages in estuarine areas having 4-5 m depth with less water currentand reservoirs and in stationary cages in shallow areas of 3-4 m depth. Cageculture of seabass can be adopted as a household or as a community - basedactivity.Asian seabass is extensively cultured in South - East Asian countries likeThailand, Singapore, Malaysia, Indonesia and also in Australia. However, in India,seabass culture is a traditional activity in the low-lying coastal areas in West Bengal,Andhra Pradesh, Tamil Nadu and Maharashtra wherein the juveniles either enteralong with tidal water or they are stocked in lesser numbers and harvested after 5-6 months.The major constraint in large - scale farming of seabass is the non-availabilityof quality seed in adequate quantity at the right time in addition to scarcity of asuitable feed. The Central Institute of Brackishwater Aquaculture (CIBA), Chennai,has developed an indigenous technology for the seed production of seabass undercaptive conditions, which can be adopted to any scale. This technology has alreadybeen transferred to Rajiv Gandhi Centre for Aquaculture (RGCA, MPEDA), throughconsultancy and through transfer of technology, to Pancham Aquo, Mumbai.

2. BIOLOGY OF SEABASSThe Asian Seabass is widely distributed in tropical and sub - tropical areas~f the Western Pacific and Indian ocean between longitude 5@E to 16@W and 24ON, 25" S latitude and found throughout the northern part of Asia, southward uptoQueensland (Australia) and westward up to East Africa. Seabass is a hardy,fast- growing euryhaline fish capable of withstanding a wide range of environmentalfluctuations.2.1 TaxonomyPhylum - ChordataSub-phylum - Vertebrata2 2 Common and vernoculor namesClass - PiscesSub-Class - TeleosteiiFamily - CentropomidaeGenus - LatesSpecies - colcarifer (Bloch)Lates colcarifer is commonly known as Asian seabass, Giant perch,Cock - up and Barramundi (in Australia). In India, it is called by differentnames in various regions.2.3 Distinguishing featuresTamil - KoduvaMaloyalam - Kaalanji or NarimeenTelugu - Pandu KaapoMarathi - JitadaBengali/Oriya - BhetkiSeabass can be easily identified with its elongated, slightly compressedbody with a deep caudal peduncle. The head is pointed with concave dorsalprofile, becoming convex in front of dorsal fin. The dorsal fin with scalysheath has 7-9 spines and soft rays with a deep notch dividing the spinyport from soft parts. The pectoral fin is short and rounded with strong

ierrotions above base. The anal fin with scaly sheath is round in shape withhree spines and 7-8 soft rays. The caudal fin is round. The mouth which islarge and slightly oblique having upper jaw with villiiform teeth reachesbehind the eye. The Lower edge of operculum with strong spine and a serratedflap above the origin of the lateral line. The body of the fish is olive - brownabove with silvery sides and belly. The eyes are brilliantly coloured.2.4 Life historyAsian seabass Lates calcariferThe fish grows in shallow areas like estuaries, backwaters and evenin freshwoters. It is catodromous in migration. It migrates to near shorewaters (30-34 ppt) during reproductive phase for gonadal maturation andMigrotion pattern of seobass

The newly hatched larvae drif in the coastal waters, estuaries andbackwaters. Juveniles even find their way into the freshwater zones. Theystay in these shallow water bodies to feed and grow. The adult fishes migrateto the bar mouth regions through estuaries and enter into the sea forspawning.2.5 Sexual dimorphismAlthough sexes are separate in seabass, it is difficult to identify thesexes. The snout of males are slightly curved than that of females. Malesare generally smaller in size (less than 3 kg), whereas females are larger.During the spawning season, the abdomen of female is relatively large andextended compared to that of males.Seabass is a protandrous hermaphrodite fish. Majority of the fishesare males when they are around 2 to 2.5 kg in size and later as they attainmore than 4 kg, they become females.2.6 Sexual maturity, spawning and fecundityThe males attain maturity when they are around 2 kg, at the age of2 + years and females around 4 kg in weight generally reach maturity after3 years.The gonad is dimorphic and develops rapidly within 3-4 months. Inmature moles, milt oozes out as a thick milky white viscous fluid when theabdomen is gently pressed. The gonodol maturity of females is classifiedinto VII stages. The fully ripe ovary occupies the entire body cavity andcontains free eggs. The ovary contains oocytes of different sizes; usually theposterior region contains larger oocytes indicative of a protracted multiplespawning behaviour. A fish may spawn continuously for 2-3 days in asingle spawning and 3-4 such spawnings takes place in a season. Thefecundity of seaboss which depends upon the size of the fish varies from 1 to20 million. The fish releases 0.5 to 2.0 million eggs in one spawning.2.7 Food and feedingAdult seabass is a voracious carnivore and predatory in feeding habit.Juvenile fishes are, omnivorous, feeding on zooplankton. As they grow, theyfeed on young fishes and shrimps. Seabass preferably feeds on sub-surface

2.8 Growthpelagic fishes and crustaceans. When food is scarce, they resort tocannibalism in young stage.Growth of seabass mainly depends upon the density, the quality andquantity of the feed available and the environmental conditions. Growth isbetter in moderate solinities of 10-15 ppt. In the first year, they grow around1.0 kg. In the second year, they attain 2 to 2.5 kg and in the third year upto6 kg. A growth rate up to 4 kg has been observed under culture conditions.Differential growth within the same age group with wide variotion is o commonphenomenon and in the process, the 'Shooters' (fastly growing ones) tend tocompete for food and space and grow to a larger size.

3. CONTROLLED BREEDING UNDER CAPTIVE CONDITIONSThe Asian seabass spends the growing phase in confined waters and migratesto the sea for maturation and spawning. Adult fishes can be made to mature andspawn under controlled conditions if the parameters like salinity, pH, water depth,light intensity etc., prevailing in the sea can be simulated in the controlledenvironment. This may be feasible in sheltered bays with clear seawater and openaccess to the sea. In such areas, if the adult fishes are maintained in cages orponds, gonadal maturation and spontaneous spawning may take place. Undercontrolled conditions, in confined tanks, by increasing water depth during hightide and reducing during low tide and also maintaining the water salinity as that ofseawater, gonadal maturation and spawning of mature fishes can be achieved.The seawater salinity plays an important role in the maturation and spawning.Gonadal resorbtion is observed when water salinity drops less than 25 ppt.3 1 Hatcherv facilitiesFor the successful production of seabass seed the following basic focilities orerequired.1. Hatchery facilities :* Hatchery building* Quality seawater source* Good freshwater source* Pumping facilities with suitable water filters to maintain water quality* Accessory infrastructure facilities like road, electricity etc.

2. Broodstock holding tanks/cages/ponds3. Moiuration tonks4. Spavning tanks5. Egg incubation tanks6. Live feed culture facilities :Axenic algal culture roomAlgol culture tonksRotifer culture tanksBrine shrimp (An'emia) hatching tanks7. Larval rearing tanks8. Nursery rearing tanks9. Packing facilities for seed disposal10.Anolytical laboratory1 1 .Administrative/living roomsThe required hatchery facilities with approximate capital cost, operationalexpenditure and returns ore given below for a seabass hatchery with a capacity ofone million seed production. These facilities ond production capacity can be scaledup as per the requirement.

Cost estimate for a small - scale hatchery of 1. calcarifer(production capacity one million seed)Noo-RecurtinBrood stock holding tanks (100 I):2nmISpawning tanks (20 t):Egg incubation tanks (500 1):ILive feed culture la*:-Larval Rearing tanks (50 t) :Algal culture tanks ( sr ).Rotifer culture tanks(% t):Live feed culture facilities A/C rooms er. (20 m2)Artemia hatching @nks(100 I)10 nos.10 nos.20 nos.680,0006,00,000I .~K),ooO40,~XX)

Recurring (Annual)1. Man power:Sr. technician: 1 no. @ Rs. 10,000lpmTechnicians : 2 nos. @ Rs. 8,000tpmLabourers: 8 nos. @ Rs. 3.0001pm(In Rs.)1,20,0001.92.0002.88,0002.Broodstock fish:Female: Average weight 5 kg(I00 kg Rs.200/ kg live fish)Transportation cost :Male: Average weight 2-3 kg( 100 kg @ Rs.2DOtkg)Transportation cost:20 Nos.40 Nos.20.00010,00020.00010.000Feed:Broodstock feed:5% ol'the body weight. Monthly requircrnent: 300 kgDaily 10 kg. @ Rs. 15000/tonnes (3.6 tonnes)Larval feed:Anemia cyst per year : 100 kg; 0 Rs. 2000lkgWeaninc dietI 4, I Fertilizers and chemicals 1 lO,(XK,5.6.7.Hormones LHRHaElectricity G?Rs. 10,000tprnFuel @ Rs, 10,000lpm8. 1 Mi~cellancc~us: Nets, plastic wares, glass wares etc., 25,000I'Total operational cost (R) 1 12,87,500IIPRODUCTION SCHEDULETotal No. of runs: 8Production of hatchling run : Total fertilized eggs from 2 spawners : 2 millionHatching @ 70% : 1.4 million hatchlings /runProduction of fry (30 days old larvae) per run @ 15 % survival : 2.10 lokh fryTotal fry production for 8 runs: 16.80 lakhsNursery rearing @60% survival of totol fry : 10,08,000 nos.Revenue realization @ Rs.2.50 per piece (C) : Rs. 25,20,000Annual net income over operation01 cost (C - B) : Rs. 12,32,000I50,0001,20.000I .20.O(K)

3.2 Seed production technology3.2.1. Broodstock developmentAvailability of viable and healthy broodstock is a pre-requisite for thesuccessful hatchery operations. Broodstock fishes have to be maintainedfor 6-8 months for captive maturation and spawning under controlledconditions.3.2.2 Broodstock procurement and transportBroodstock fishes can be collected from the sea or from the culturefarms. Seabass is caught using gill net, seine net or hook and line, the lastone being the most commonly used gear. Fishes showing external/internalinjuries, loss of scales and damage in the jaw, snout and opercular regionsshould be avoided. They should be checked for pathogens, quarantinedand conditioned for transport. Tanks lined with soft materials should beused for transport to avoid iniury to the fishes. Fishes in the size range of2-3 kg for males and 5-6 kg for females con be procured The ratio can bemaintained as 2:l for smaller and larger fishes.

I AcclimatisationThe fishes should be acclimatized and quarantined for a period of5-7 days in the hatchery before releasing them into the holding tanks.Prophylactic treatment with 1 ppm Acriflavin and / or 5 ppm of potassiumpermangonote for one hour is desirable to avoid further infection. Afterscreening for pathogens, the fishes are released into the'holding tanks andmaintained.3.2.4 Broodstock holding facilitiesBroodstock fishes are held in 500-1 000 m2 ponds containing clearseawater to a depth of 2m or in floating net cages in the open sea or shelteredbays. In places where this may not be feasible, separate RCC holding tanksof 12 x 6 x 2 m dimension with water holding capacity of 100 t is advisable.The tanks should be designed with provision for water inlet and outlet. Theinlet facility should be in such a manner as to fill the tank within 1 hr and thedrainage of water from the tank should be possible within % hr. The tanksmay be covered with roof structures or may be kept open. In the case ofopen tanks, algal bloom will appear due to exposure to light and the tankshove to be cleaned daily to maintain water clarity and quality.3.2.5 Broodstock maintenance~~ro~u\~och t\oldlr?g toi\i>Maintenance of captive broodstock requires constant attention forproviding good quality water, feed and routine health monitoring of broodfishes which can ensure healthy seed production.

3.2.5.1 Water quolity manogementThe seawater used in the hatchery should be clean and free from silt.It is desirable to construct the hatchery away from inland water dischargepoints because the water may contain agricultural/dornestic/industrial wastesand the salinity may decrease considerably. The f~uctuation of salinity shouldbe minimum at in the selected site. Water drawn from the open sea or froman intertidal bore well is desirable for broodstock maintenance.The optimum range of water quality parameters for broodstockmaturation and spawning areTemperotureSalinitypHDissolved OxygenAmmoniaNitratePhosphateSuspended solids- 28 - 30°C- 28-33 ppt- 7.0 to 8.2- 5-7 ppm- less than 0.1 ppm- less than 0.01 ppm- less than 10-20 mg/l- less than 2-5 mg/l3 2.5 2 Feed monogementAs seabass is a predatory fish, feeding mainly on live fishes/shrimps.brood fishes may also prefer the same type of feed. However, it may not bepossible to provide live fishes ot oll the times. Moreover, if the live fisheshave any pathogens, the brood fishes may also get infection. To avoid this,fishes can be weaned to feed on frozen fishes. Low - value fishes like tilapiaand oil sardines can be procured from the commercial catches, cleaned,packed in 2-3 kg pockets and stored in a deep freezer. The frozen fishes canbe thawed and fed @5% of the body weight, doily, in the evening hourseither os whole or as cut pieces. In the beginning, the seaboss brood fishesmay be reluctant to feed on the inert diet. However, it can be weaned to thisdiet over a period of 10- 15 days.

IBroodstock feed - trash fishesI. > m3 2 5 3 H~olth managementBroodstock fishes maintained in captivity may be infected withecto-parasites like monogenic trematode D~lectonum lotes~;; Gyrodo~lussp., the crustacean parasites Coll$us, Lemothropusetc. especially during theperiod from November - February. When the ambient water temperature

is lower, to control parasite infection, treatment with 100 ppm formalin forone hour in case of lesser intensity or 1 ppm of organophosphorus pesticideDichlorvos, when the infestation is heavy, is recommended.CalU taus sp.

3.3 Maturation and spowningFishes maintained under optimal water quality conditions with good feed andhealth management, mature spontaneously under captivity. However, a virginbroodstock may respond after a year or so and thereafter the maturation is anannual phenomenon during the spawning season (May to October in Tamil Nadu).Salinity is found to play an important role in the maturation of seabass. Gonadalresorbtion is commonly observed below 25 ppt. By maintaining the salinity andtemperature at optimal levels, seabass can be made to spawn year - round.Under captive conditions, matured seabass spawns spontaneouslyand profusely. Controlled breeding can be ochieved through environmentalmanipulation by simulating the conditions in the sea, like raising and reducing thewater level as during tides, maintaining temperature between 28-30°C and salinityaround 30-32 ppt. However, this may not be feasible everywhere. Hencespawning is induced through administration of hormones. The importanthormones used for induction of spowning in fishes are carp pituitary hormone,salmon pituitary hormone, LHRH analogue, human chorionic gondadotrophin(HCG), ovaprim, pimozide, puberogen, ovatide etc. In the Asian seaboss,LHRH-analogue is found to be effective with assured success.3.3.1 Selection of breedersGravid female fishes (above 4 kg) with ova diameter of more than 0.450 mmand oozing males (of size 2.5-3.0 kg) are selected in the ratio of two males to onefemale. The gonadal condition is assessed by ovarian biopsy of females which iscarried out by reducing the water level in the broodstock tanks and collecting thefishes with a soft seine net/hapo cloth for assessing their gonodal condition. Thefish is securely which is held and turned upside down to moke it docile. A polythenecannula (1.2 mm in diameter) is inserted into the oviduct and pushed 10-1 2 cminside. The other end, which is held outside is aspirated by gently pulling out thecannula. The contents are emptied into a petri dish. The eggs are placed in a glassslide and the ova diameter is measured with an ocular micrometer. In maturemales, the milt will ooze out when the abdomen is gently pressed.

:ac a,.,.. *-3.3.2 Induced spawning techniquesOva! Ian i-jiop~ySince, spowning of seaboss under natural conditions coincides with the lunarperiodicity, full moon or new moon days are preferred for induction of spowningwhich is usually done in the early hours (the previous day to full or new moon).

The selected breeders are administered with a single dose of LHRH-a~~rmone, intramuscularly, just below the dorsal fin and above the lateral line360-70j~/kg body weight for females and 30-35pg/kg body weight for males.Grov~d seoboss

The hormone is administered in the early hours of the day and the fishes are thenreleased into 15-20 t spawning tanks containing clean and aerated seawater. Thefishes spawn after 30-36 hours of hormone iniection, late in the evening hours.Pre-spawning responses observed are extended belly and courtship behaviour i.e.males moving very closely with females with swift movement just prior to spawning.Spawning is spontaneous; the female and male fishes release the gametessimultaneously. Fertilization is external. The fertilized eggs are transparent andfloat on the surface as granules. The diameter of the fertilized eggs will be around0.80 mm. The unfertilized eggs will be opaque and sink to the bottom. In onespawning, seabass releases 0.5 to 2 million eggs depending upon the size andcondition of the fish. Second spawning during the subsequent day will also occur.The same fish can be induced to spawn after 2 months.3.3.3 Egg collection and incubationThe fertilized eggs are collected from the spawning tanks using sieve netswith less than 0.50 mm mesh size or bolting cloth or collected through over -flowing method or siphoning method. Automatic egg collectors with airlift systemcan also be installed by means of which the eggs will drif into the bag nets throughaeration. The eggs are randomly counted and transferred to incubation tanks.Collection of eggs25

Cylindro - conical fibre glass tanks (FRP) are preferable for hatching. Eggsare kept @I00 no./l in 250-500 1 tanks for incubation and hatching. Followingembryonic development, hatching takes place 16-1 7 hours after fertilization. Thehealthy larvae are collected and transferred to the larval rearing tanks.3.3.4 Embryonic developmentThe fertilized egg undergoes various stages of development before hatching outas a larva. The stages of development ore briefly mentioned below :

Gostrulo stage27

4. LARVAL REARINGThe newly hatched larva is 1.4 mrn in size with a yolk sac. The larvae aretransferred to rearing tanks of 4 - 5 t capacity. They undergo metamorphosis andthe mouth develops on the 3rd day. Clear seawater devoid of pathogens andcontaminants is a prerequisite for larval rearing..Therefore the source water ispassed through biological filters, pressure sand filters, U.V. filters and cartridgefilters before if can be used in larval rearing units.4.1 Collection of larvae and stockingHealthy larvae collected from the incubation tanks are randomlycounted and transferred to the rearing tanks. Since, seabass larvae arephototrophic, a light source can be used to attract them by covering the entireincubotion tank with a black cloth except for a smoll area which is kept openfor the light to pass. The larvae congregating in the lighted area can be gentlyscooped and transferred to buckets contoining a known volume of water. Aliquotsamples ore then taken randomly and the total number of larvae are counted.The larvae ore stocked in the rearing tanks @ 30-40 no/l.

Hatchling - 1 day oldHatchling - 2 days old30

Larval feedMouth formation - 3 days oldThe larvae start feeding from the 3d day onwards. Rotifers (Bmchionusplicotilis, B. rodenfiformes) are ideal food for early stages because of theirsmaller size (around 100 micron) and nutritive value. After reducing the waterin the rearing tanks, fresh rotifers are collected, washed, sieved using suitablemeshed bolting nets and introduced @ 20-30 nos ml into the larval tanks.Rotifers are fed from the 3rd to the 9" day and every day their density in thelarval rearing tanks is measured and the feeding rate is accordingly adjusted.By the lofh day, the larvae reach 2.3 to 2.5 mm and their mouth widens toingest feed of size 200 micron and above. Hence, from 10" day onwardsalong with rotifers, brine shrimp, Artemio nauplii are also introduced @ 2-4nos. ml. This combination feed is supplied up to 15'" day, by which time thelarvae attain 4 to 5.0 mm size. From 1 6Ih to 25'" day, the larvae are exclusivelyfed with Arfemio nouplii at a density of 4-6 nos ml. Since the nutritionalquality of rotifers or Artemlomay not be adequate in some instances, enrichmentwith PUFA media (like SELCO) is also done to enhance their nutritional statuswhich is essential for the seabass larvae. By 21" day the larvae will be around10 to 1 1.0 mm and by 25'" day, the fry reach 1.3 to 1.5 cm in length. The fryare supplied to enterprising farmers to rear them to stockable size in farms.. .The fry can also be reared in the hatchery upto fingerlings stage and suppliedto the farmers for stocking in grow - out systems.

4.3 Water changeSeabass larvae are reared under the green - water culture system.The water in the rearing tanks is changed daily @40-50% by using suitablemeshed nets to prevent the escape of larvae. Fresh and filtered seawateralong with green water (containing species of Chlorelh / lsochrysis /%frose/mis/Nann~h/oropsis) are also added to the rearing tanks and thealgal cell density is maintained around 20,000-30,000 cells/ml. Additionof green water fecilitates the conditioning of the rearing medium andmaintains the water quality by reducing ammonia. The green algae alsoserve as feed for rotifers.4.4 Live feed cultureLive feed includes the a lgal species like Chlorella, Nannochloropsis,lsochrysis, %fmselmis, zooplankton like the rotifer Brachionus sp. and Aderniunauplii. Both larval rearing capacity and live feed rearing capacity aremaintained in equal proportion in the hatchery. Pure algal cultures maintainedin axenic culture facilities are transferred to mass cultures tanks, fertilizedwith ammonium sulphate, urea and super phosphate @ 100 g, 10 g andlog per ton of water, respectively. The algae are harvested in 36-48 hoursand use as feed for the rotifer. Rotifers are continuously maintained as stockculture and inoculated regularly into the tanks filled with filtered seawater.They are fed with algae. After 6-7 days, rotifer density increases considerablyand they are harvested using 40p mesh plankton net, washed and fed to thelarvae. Continuous cultures of algoe and rotifers are to be maintained inthe hatchery to ensure uninterrupted feeding which is very crucial for successful

lsochrysisNonochloropsis

Rotifer cystsRotifer34

4.5 Production of Ariernia noupliiArtemia cysts available commercially are dormant eggs and whenkept in sea water they hatch out as nauplii. Transparent funnel shapedcontainers, aerated from the bottom, are used to achieve best hatchingefficiency with high densities of cysts. The hatching contoiners are cylindroconicalFRP tanks of 20-30 1 capacity. The hatching tanks are illuminatedfrom a distance of 20 cm with 60-watt fluorescent lamps. Continuous aerationfrom the bottom of the hatching tank ensures that the cysts are kept insuspension. Hatching is complete within 24-36 hrs and using a light source,the nouplii can be congregated and collected by siphoning.Artemio nouplii

As the seabass larvae grow, the requirement of feed in quantity and sizeincreases and this can be met by Ariemia biomass. An'ernia biomass productionunder controlled conditions can be carried out either in batch or in flow-throughculture systems. For high density culture in both the systems, provisions have to bemade to maximize oxygenation of the medium and availability of food to nauplii.In batch - culture system, nauplii are reared upto adult stage in airlift racewayswithout water renewal. Freshly hatched nauplii are stocked @ 10,000 nos. / I andfed with rice bran iuice. The water transparency is maintained at 15-20 cm. Beinga non selective filter feeder, Ariemiu can be cultured using a wide range of feedslike Choetoceros, Skeletonemu, marine algae, rice bran iuice, yeast etc. SinceArtemio is a continuous filter feeder, adequate food must always be available in themedium. Faecal pellets and excreta are to be removed regularly from the culturemedium from the 4Ih day of culture. pH of the water should be maintained above7.5. Harvesting is done with a scoop net. Intensive Artemio culture at a highdensity of 20,000 nauplii/l can be achieved with flow-through system with continuousrenewal of water, but in all other aspects it is similar to batch culture system.

5. NURSERY REARINGRearing of the seabass fry to stockable size in grow-out pond is essential toproduce uniform size and healthy seedlings that will ensure promising growth, bettersurvival and higher production. Nursery phase, being transitional can be used forocclimatiz~ng the fish to the environmental conditions and also condition them tothe feed proposed to be used in the growout culture system. Though seabass is ohardy fish with excellent qualities to adapt to the environmental changes, handlingond transport stress, they are highly selective in feeding. Their natural tendency ofdifferential growth hierarchy, social dominance and cannibalistic behaviour are theiactors responsible ior their less survival in nature as well as in controlled conditions.It is very difficult to condition the young fishes to accept a new diet. They resort tostarvation rother than easily accepting a new diet. Nursery rearing can be done inseparate tanks in the hatchery or open ponds or cages or hapas with in the growout~ond itself. Constant monitoring, coreful handling, grading and providingquality feed in adequate rotion are some of the requirements for their successfulnursery rearing.Due to their natural differential growth, there will be more than onesize group of seaDOSS in the rearing tonks within the some batch itself. Thelarger ones ore colled 'shooters' and they consume more food, occupy morespoce and with high growth characteristics tend to dominate the smallerones. Being predators, they use their size advantage to chase away thesmaller ones to toke away lion's share of food and space in the tanks,causing constant threat to the smoller ones by not allowing them to feedand thereby make them weak. Exploiting this situation, the large fish preyupon the smaller ones. This sort of cannibalistic behoviour is seen evenfrom early stages Experiments have proved thot even by intensive feedingwith des~rable live feed like Artemlb nouplii, predation by lorger ones overthe smoller ones cannot be avoided. The more the size difference, more therate of predation. The only way to ovoid this problem is to maintain uniformsized fish in the rearing system. The process of segregating the differentialsize groups and maintoin uniformity is called as grading.Mechanical graders with adjustable pore slze or manual sieves withsuitable mesh net are used to grade seabass try. The larger ones will beretained at the top with larger mesh sieve, medium sized ones at the middleand the smaller ones at the bottom. Then the segregated fry are introduced

into separate tanks for further rearing. Grading should be done once in3 days, otherwise, the end product will be very few larger specimen, whichwould have fed thousands of their own.,~lcl of fry5.2 Nursery r2orlng In hofcher~esCannibollsm among larvae20-25 days old fry in the size range of 1.5-2.0 cm are stocked in 5 to10 t circular/rectangular RCC/FRP nursery tanks provided with inlet andoutlet facilities and covered with suitable mesh net and connected to bothfreshwater and seawater pumping facilities. Flow-through provision isdesirable, which can simulate the natural condition in the tanks. Water depthshould be maintained between 70 and 80 cm with sufficient aeration.5.2.1 StockingSeabass fry can be stocked @ 1000 no/m3 in the nursery tanks.Stocking of different size groups will lead to differential growth and formationof shooters. Hence, uniform size of fry should be stocked in the nurserytanks.5.2.2 Feed monogement (Weoning)Feeding is the most critical aspect in the nursery rearing of seabass.As mentioned earlier, seabass are highly selective and addictive in feeding

habit. It may be difficult to weon them to any new diet, but it is required.During larval rearing, because of their inability to ingest and digest inertfeed, they are fed with live micro zooplankton. However, as they grow,adequate quantity of feed is to be provided which may not be possible withmicro zooplankton in the hatchery. The fry have to be accustomed to feedon inert diets and this transitional feeding is to be done with at most care.The live diets should be gradually reduced and quality inert diet should besubstituted @20%, 30%, 50%, 70% and 80%, so that over o week the frycan be made to solely depend upon the inert diets. Live feeds like Ariemianauplii and biomass, copepods, clodocerans like Moho are also preferredsince they can be ingested easily and contain more than 50% protein. Since,the fish is habituated to feed on moving live animals, their natural feedingbehaviour is taken care by these live feed. Production, transportation anddistribution of large quontity of live feeds will be difficult. Hence, the fishhave to be weaned to inert artificial diet. The diet should be acceptable,attractive with apt particle size and palatable. For detritus feeders andomnivores (like shrimp) which are non selective in feeding habit and canfeed either from bottom or surface, the buoyancy of feed is not very important.However for selective feeders like seabass which prefer to feed on movingzooplankton, small fishes and shrimps in water column, buoyancy and shapeof the feed are important.Seabass nursery feed as extruded floating pellets in granular formswith 0.2 mm particle size onwards is available. ClBA has developed aweaning diet for seabass. The feeding rate is adjusted ad Lbiturn in thenursery tanks. During initial period, feeding rate can be upto 50% bodyweight which can be reduced to 20% towards the end of nursery rearing. Frycan also be fed with cooked and minced fish/shrimp meat passed through2-3 mrn size mesh sieves. The meat particles are allowed to settle and fed

od libitum at an interval of 4-6 hr. Since juvenile seabass is a voraciousfeeder, adequate feed should be made available in the rearing facilities.Excess feed should be removed from the bottom after 2-3 hours of feedingbefore introducing fresh feed.5.2.3 Woter qvolity monoyementMointenonce of water quality in the nursery tanks is very importantfor the production of healthy seed. Flow through facilities are highly desirable;otherwise every day after the removal of debris, 40% of the water should bereplaced with fresh filtered water. It is observed that seabass grow betterbetween 15-20 ppt salinity and hence the salinity in the nursery tanks shouldbe adjusted to the above levels by adding freshwater or brockishwater.5.2.4 Health monoyernentEventhough juveniles of seabass ore very sturdy, they are highlysusceptible to bacterial, fungal and viral infections. Bacterial diseases arecaused by Vibrio onguillarum, 1! olginolylcus, Kharveyi. Infected fry willcongregate in the corners of the rearing tanks and stop feeding and will beemaciated in appearance. Treatment with 10 ppm Furozolidone is found tobe effective if the infection is detected early, otherwise it will lead to rnortolity.Parasitic diseases include infestation of protozoons such asChilodonella sp. and Fichodina sp. Behaviourol changes like congregationand blackening of the body are the symptoms. Treatment with 50 ppmformalin is followed which will control further spread of parasitic diseases.Noda virus (VNN Virus) infection has olso been observed in the fry.In the nursery tanks, the fry attain a size of 4 to 6 cm in 25-30 days. Inponds, the fry are reared till they attain 1-2 g and in cages rearing is donetill they reach the size of 10-20 g with an average survival rate of 50-60%. Inwell managed nursery tanks survival upto 92% can be obtained.5.3 Nursery rearing in open tonks,'pondsSeabass fry can be reared in open tanks or ponds of 200-300 m2 withfacilities for water exchange. Inlet and drainage pipes should be guarded

with suitable net screens. Extensive rearing of fry can olso be done in eitherponds or tanks in the farm area. Although frequent grading of the fry maynot be feasible, nursery rearing in pond will be cost effective with naturalfeed. However, in earthen ponds the survival rate may be poor and therecovery may also pose problem. Ponds with concrete flooring will ensureeasy collection of the seed without any injury or damage.5.3.1 Nursery pond preparationNursery ponds are prepared by following the routine management protocolslike drying and tilling the ponds. The pond is then manured with raw cowdung@10,00Okg/ha and fertilized with urea and super phosphate for enhancingalgal and zooplankton growth by keeping the water level to 50 cm. After10 days, the water level is increased to 0.75 - 1.0 m and the fry can beintroduced.5.3.2 Arfemio biomass production in the nursery rearing ponds .Artemio biomass can be produced in situ in the nursery pond at 30 pptsalinity. In a well prepared nursery pond with rich algal bloom, An'emiocyst @ 1 kg/1 00m2 can be introduced. Nauplii will hatch out from the cystduring the subsequent day and grow by consuming the algae. Substantialquantity of Artemia biomass (pre adult population) will be available in thepond after 11-12 days. At this stage, seobass fry can be stocked.5.3.3 StockingA,ii.'?.c: !,,,,~,,(., ;,Healthy fry of 1.5 to 2.0 cm size are stocked in the open ponds @200-300 no/m3.

5.3.4 FeedingThe fry are fed with supplementary feed like minced fish/shrimp meatprovided in suspended trays in the corners of the pond. Feed applicationand schedule of feeding can be programmed as being done in the hatcheryrearing of the larvae.5.3.5 Water changeM~nced i~sh meat ballsThough seobass juveniles con tolerate wide range of salinity, it isadvisable to reduce gradually the salinity in the rearing ponds by 2-3 pptdaily to avoid stress. The optimum salinity for seabass rearing is 15 ppt.Water exchange @ 40% with brackishwater/seawater should also be doneon alternate days.5.3.6 Growth and survivalSince open pondhank nursery reoring system is more natural with sufficientquantity of natural food organisms the fry will grow fast to reach stockingsize of 3-59 within 30 days. However, there will be differential growth, sincefrequent grading may not be possible in ponds as done under controlledconditions. A survival rate of 40-50% can be achieved in a well managednursery pond and this will further reduce in case the pond is not monagedproperly.5.4 Nursery rearing in cages/hopasRearing of seabass fry can be practiced in floating net cages / hapas fabricatedwith suitable meshed net. This method is advantageous to other methods

ecause the installation of net cages will be cheaper, management is easier,close monitoring is possible and also solves the problem of competition forspace. Collection of reared seed and grading can be fast and easy. Thecages may be square or rectangular in size ranging from 4 to 10 m2 initiallyand can be increased to 15 to 20 m2 at later stages. The net cages can beeither floating or stationary.5.4.1 Floating net cagesNUISCI~ I(,CI~ ti^^ 111 I>c-,\.ILI:Floating net cages are used for rearing fish in ponds and canals havingmore than 3 m water depth. They are hung from floating structures made ofbamboo or wood frames using styrofoam blocks or polypropylene tubesfastened to poles and set in shallow waters. The frames are anchored. Theend of the cages are fastened to sinkers of required weight to keep themfloating. The cage can easily be transferred to convenient and suitable placesfor operation. The cages can be brought near to the edges of ponds orcanals for close monitoring and collection of seed.

5.4.2 Stationary net cogesStationary net coges are fixed in a particular place. The cage is fastened atthe bottom and surface to poles at its four corners. These cages are used inshallow waters of less than 2m water depth.5.4.3 Monogement of cogesThe cages, either floating or fixed will offer natural condition for thefishes to grow. However, there are chances of mesh clogging due to theadherence of debris or weeds which restrid water movement, resulting instagnation of water and accumulation of waste products in the cages. Toavoid this problem, cages should be cleaned daily using soft brushes. Theyshould be checked for damage by crabs. It is preferable to have two layeredcages to avoid such risks. Initially 2 mm mesh net may be used to preventthe entry of other pests or predatory fishes and the escape of fry from thecages. At later stages, mesh size con be increased according to the size ofthe fish .Fry of 1.0 to 2.0 cm size are stocked @ 80-1 00 nos/m2 initially andas they grow the density can be reduced to half, once in 15 days so that by30-45 days the density will be maintained between 25-30 nos/rn2.The fry are fed with minced/chopped meat of low cost fishes liketilapia or shrimp in fresh condition. Floating extruded pellets are also usedto feed them. The feeding rate followed is 100% of the biomoss with freshfish/shrimp meat or 20% of the body weight for floating pellets. Daily thefeed is supplied in two doses in the morning and evening hours.5 4 6 G~owth ond surv~voiIn 30-45 days, the fry will attain 5-1 0 cm size. Survival rate as high as 80%can be obtained from well managed coges.

6. PACKING AND TRANSPORT OF SEEDSeabass frylseed can be transported to any distance without any probleminvolving even 18-24 hrs of transport. The mode of transport, containers, stockingdensity of the seed etc depend upon the size of the seed and the distance to betransported.Three days prior to transport, the salinity of the rearing tank is adjusted asthat of nursery or grow out culture system where the seed will be furtherrearedlreleased. The water should be clean. After removing weak andsuspected diseased seed they are graded and uniform size groups are kept inseparate containers for 48-72 hrs for acclimatisotion before transport.6 2 Seed countSeabass seed are transported either in fry or fingerling stages. Seed con becounted by any one of the following methods.6 2 1 Sample countSince the fry are too small they can not be individually counted. Hence, aftercollection, they are placed in o known volume of water and with gentle mixingrandom aliquot samples are taken and counted individually. The averagenumber of fry per unit volume and then the total number in the container canbe calculated. From this known volume, the required numbers can betransferred into the seed bogs.1 2 2 Visual couniThis method can be followed for counting medium sized fry which are moreor less distributed uniformly in a container,. In a known volume of water, thefry are individually counted and released. The quantity of the seed in thecontainer is visualized and a iudgment is made for their total number.

6.2.3 lndividuol countFingerlings (more than 2 cm) can be individually counted and released in tcthe container.6.3 PackingSeabass frylseed are transported in open containers like plastic buckets, bags,bins, carboys etc. for shorter distances involving less than 3 hrs oftransportation.For long distance transportation, packing is done in air tight carriers underoxygen which needs the following items:Oxygen cylinder with regulatorPolythene bags of 40x60 cm size with 0.1 1 m thicknessInsulated - thermocole boxes/styrofoam boxesRubber bandsCrushed iceSaw dustClean treated water having salinity as thot in which the fry are released/or proposed to be transportedArfemia nau~liiThe polythene bags are first tested for leakage and filled with 1 /3 of thevolume with clean water (around 5-6 litres). Uniform size seed are thenintroduced carefully into the bag. The oxygen drawn from the cylinder isbubbled in the woter for 2 minutes for its dissolution in woter. Then the bagis inflated with oxygen by firmly holding the bag. The oxygen filling tube isswiftly removed from the bag and the mouth portion of the bag is twistedand tied firmly with rubber bands. The bag is then immersed in water andboth the ends are tested for any leak. The quantity of seed and salinity of thewater are labeled on the top of the bag. The packed bag is placed insidecartons or styrofoam or thermocole boxes.Crushed ice packed in small pouches or mixed with saw dust are placed onthe sides of the seed bag inside the cartons/boxes to reduce the wotertemperature. During transportation, temperature of the container may raise3-4°C above ambient temperature due to the build up of the carbon di oxideinside the bag due to the metabolic octivity of the fishes. Increase in

temperature leads to less diffusion of oxygen, reduction in pH, water qualitydeterioration and mortality of seed over longer duration. It is always advisableto maintain the temperature around 20°C during transportation so that thefish will be less active producing less metabolic wastes. If available, dry icecan be used for reducing the temperature more effectively.i'acl

6.4 Mode of t~ansportFor long distance transportation, freight by Air is desirable since it takes lessertime and reduces stress to the seed leading to good survival rote. For distances lessthan 500 .km involving shorter duration of 6-1 2 hrs, transportation can be done byrail or road which will be cost effective. To areas requiring less than 3 hrs durationseed can be transported by road in open containers with bubbling of oxygen.At the end of transportation, the fish would have become acclirnatized to theconditions in the bag like higher concentration of CO,, NH, and reduced pH. Thefish seed should be acclirnatized to the conditions of the rearing pond before stocking.After opening the bags, the water is gradually added @lo% of the volume once inevery 5 minutes and within 30 minutes the bog will contain 75% new water and25% transported water. The bag should not be aerated since this will eliminateCO,, increase the pH and the free ionized ammonia will be converted in to unionizedammonia causing more toxicity to the fish, leading to stress and mortality.After acclimatisation, the fish can be stocked in the grow out ponds or nurserycages or tanks for further rearing.

7. CULTURESeabass is extensively cultured in Thailand, Malaysia, Singapore and Australia.In India, it is cultured in a limited scale in the traditional farms in coastal area.Compared to carp culture or shrimp culture, seabass culture is a small propositionand the main reason being that while the market for shrimp is global, the marketfor seabass is largely regional. However, seabass is the only species that is mostcommonly farmed amongst the finfishes in South-East Asian countries because itsseed can be produced in the hatchery throughout the year at reasonable price.Based on case studies, it has been estimated that in Thailand the production rate ofseabass was 20.5kg/m3. It fetches USf2.27 per kg. Seabass con be consideredcomplementary to shrimp for: the sustainability of brackishwater aquaculture. It canolso be a species for freshwater aquaculture.7.1 Troditionol cultureExtensive culture of seabass as a traditional activity is followed in theIndo-pacific region. In low lying coastal ponds, juveniles of assorted sizescollected from estuarine areas are introduced and fed with the forage fisheslike tilapia, shrimps and prawns available in these ponds. These pondsreceive water from adioining brackishwater or freshwater canals or frommonsoon flood. Harvesting is done after 6-8 months of culture. Sinceseabass exhibit differential growth, the size of the harvested fishes vary from0.5 to 5.0 kg. Production upto 2 ton / ha / 7-8 months has been obtained.7.2 Improved seoboss culture methodsThe traditional culture of seabass can be improved by stocking uniformsized seed at specific density and feeding them with low cost trash fishes/formulated feed. Water quality is maintained through periodic exchange.Fishes are allowed to grow to marketable size and harvested. Seabass culturecan be done in more organized manner as a small scale/large scale activityin both brackishwater and freshwater ponds and also in cages.7.2.1 Pond culture of seobassSeabass culture in ponds can be carried out either by polyculturemethod or by feeding with low cost fishes like tilapia/oil sardines or withextruded floating pellets.

.I( :I!,( ,S CLJ 'offt pC)llc!7.2.1 .1 Poly culture methodPolyculture is an improvement over the traditional method of culturingseabass. In polyculture, the feed in the form of forage fishes is producedin the culture pond itself and the fishes prey upon them as and when theyrequire.7.7.1 2 Pond preparot~onThe pond is at first dried, tilled, leveled and manured with raw cowdung @ 10,000 kg/ha. If required, lime is added @ 50-200 kg/ha tomaintain soil pH above 7. Urea @ 100kg/ho and super phosphate @ 50kg/ho can also be added to enhance the algal bloom. Seawater/freshwateris then filled to a depth of 60-70cm in the pond. When the pond waterbecomes light green in colour indicating sufficient development of algaein the pond, forage fishes are introduced.7.2.1.3 For-age fishesForage fishes that can be used as natural feed should have thefollowing characteristics:Prolific breeding habitShould not be a predatorMay be a pest in the culture system

Should occupy lower strata in the food chainPreferably herbivorous/omnivorousMay not be fast growing but can adopt to high stocking densityShould be acceptable to seabossTilapia - Oreochromis mossambicus qualifies as a foroge fish.7.2 1 4 Stocking of forage fish/feed fishJuveniles to pre-adults of tilapia ore introduced @ 20000-25000 /ha into the pond one month in advance to stocking of seaboss. Theaverage weight of tilopio should not exceed 30 g to maintain its biomossto 600 kg/ho at the time introduction. The water level is maintainedaround 80-90 cm. Subsistence level of feeding is followed with rice branand ground nut oil cake @2-3% of the biomoss. Being a prolific breeder,different size groups like hatchlings, fry, fingerlings, juveniles and adultsof tilapia will be available in the pond at any given point of time.7.2.1.5 StockingIn ponds with natural forage feed, seabass of 2-3 g size are stocked@ 10,000 to 20,000 no./ho depending upon the woter and feedmanogement to be followed.7 2.1.6 Pond manogementThe woter level in the pond may be maintained to lm and 40%water exchange may be done once in a week to keep the water quality.Supplementary feeding may be continued to maintain their stock as feedfor seaboss.Since, seabass has higher growth potential than the forage fishes,they will dominate in the pond. After 3-4 months there may not be anyforoge fish in the ~ond because of complete grazing by seaboss. At thisstage, fresh stock of forage fishes should be introduced.7.2.1.7 Production and economicsSeaboss produdion of 4.0 t/ha/l 1 months was achieved from apolyculture experiment. Seabass fry of 1 .O cm reared in hop0 attain average

size of 1 g in 30 days. In a 1.0 ha pond 8,000 seed were stocked ancreared following the polyculture method. After 7-8 months, the fishesreached an average size of 740 g, (range 300 to 1500 g) with a recoveryrote of 68%. The total expenditure incurred was Rs.62,286 and therealizotion was Rs.2,37,000 with a profit of Rs.1,74,714/-.7.2.1.8 Advantages and disadvantages of polycultureAdvantagesDisadvantagesThis method is almost similar to the natural productionsystemFish can feed depending upon its requirementSince the live fish only serve as feed, maintenance ofwater quality is easier. There is nb contamination fromieft over feed.Cost effective.= Not feasible in all placesThe forage fishes like tilapia are used as food fishes insome places and their use for raising seabass willdeprive their availability to consumes.

The possibility of consumption of more forage fishes bysome seabass will leod to differential growth amongthem and thereby affect the overall production.' 2 2 Pond culture of seaboss with supplementary feeding7.2 2.1 Trash fish feedingSeabass seed of 2.0 g and above are stocked @ 10000-20000 / hain a well prepared pond with 1.0 m water depth. The fishes ore fed withminced trash fish meat made into smoll bolls and placed in trays, kepthonging in 4 or 5 places in the pond. The fishes are fed adhiturn, but notexceeding 100% body weight on wet weight basis initially and reducedgradually to 10% during the last phase of culture. Daily they are fed twicein the morning and evening hours.The feed quontiiy has to be odiusted according to the intake afterchecking the feed trays. A general guideline for the feed ration for wet fishand compounded extruded floating pellet is given in toble below.7.2.2.2 teeding with formulated feedBeing carnivorous, seabass needs a high protein diet and this is ensured byaddition of more than 60% animal ingredients in the diet.

The nutriiional requirement of seaboss is as followsProtein : 55%Lipid : 15%Fatty Acids 2%Carbohydrates : 15%The fish normally prey upon the fishes and shrimps moving in the watercolumn (pelagic). Hence the feed pellet should be of slow sinking natureand should be available in the water column for reasonable time so thatthe fish can ingest the food before it settles at the bottom. Extruded feedpellets fulfill these requirements. Further wastage of feed is less anddigestibility will be good due to pre cooking. The feed mixture can containhigh moisture and its flavour can be retained with addition of fish oil. Thesize of the pellets vary from 2.0 to 6.0 mm as per the size of the fish.7.2.3 Production and economic viabilitvSeabass (average size : 1.0 g) stocked @ 5000 / ha in a pond and fed withlow cost fishes like oil sardines and horse mackeral reoched the size rangeof 517 to 12009 (average : 947 g) in 11 months. The recovery rate was96% and the production was in the order of 4.36 t/ha. The realizotion wasRs.3, 61,585/- with an expenditure of 3,14,800/- . The profit over theoperational cost was Rs.46, 785/-7 3 Grow out culture of seabass In cagesFish culture in cages has been identified as eco-friendly intensive culturepractice for increasing production. Cages can be installed in open sea or incoastal areas; the former is yet to be developed as a commercial activity inmany countries, but cage culture in coastal areas has already established asa household activity in many of the South East Asian countries. India hasabundant potential for cage culture in the lagoons, protected coastal areas,estuaries and creeks.Cage culture can be done at high stocking density, with high survival rate. Itcan be adopted to any scale with eosy management. In cages, feeding canbe controlled and the heahh of fishes can easily be monitored. Depth and

water current are important fadon for installation of cages. Even in areaswhere the topography of the bottom is unsuitable for pond construction,cage can be installed. Harvesting is inexpensive and can be done as perthe requirement of the consumers. Above all, cage culture needs low capitalinput and the operating costs are also minimal. Cages can be relocatedwhenever necessary to avoid any unfavorable condition.3.1 Design of cagesGrow out cages of 20 m2 or 50 m1 area are fabricated with polyethylenenetting with mesh size ranging from 2 to 8 cm depending upon the size ofiuvenile fishes to be stocked. Cages can be either floating or stationaryones.7 3 2 Float~ng inel cagesThe net cages ore attached to wooden frames kept afloat using plasticdrums. Anchors or concrete weight blocks as anchors can be placed at thebottom corners of the net cage. These types of cages con be installed inareas with more than 4 m water depth but with feeble water current.These are fixed enclosures which can be installed in shallow waterareas in lagoons, brackishwater lakes etc. having 2-4 m depth. The fourcorners of coge net is fastened to wooden poles erected in the water system.The cages can be initially stocked @25-30nos/m1 with fishes of 10-15 g and after 2-3 months, when they attain 100-150 g, stocking densityhas to be reduced to 10-12 nos/m2. Cage culture is normally done in twophases. The first covers 2-3 months till fishes attain 100-150g sizeand the second lasts 5 months afterwards till the fishes reach 600-800g.

7.3.5 Feeding in cagesin the cages fishes can be fed with either extruded pellets or low cositrash fishes. Feeding is maintained around 20% initially and reduced to10% and 5% gradually in the case of trash fish feeding and with pellet feedingit is kept around 5% initially and brought down slowly to 2-3% at later stages.FCR of 6 - 7 and 1 - 1.2 are reported with low cost fish and pellet feeding,respectively.7.3.6 Cage managementSince cages are kept inside the water and exposed to water current,the net will get clogged by debris, fouling organisms etc. restriding waterexchange. Crabs may also damage the nets. The cages should be regularlychecked for clogs and leaks and damaged nets should be repaired or replacedto prevent escape of fishes.7.3.7 ProductionDue to intensive stocking and proper management, seabass productionwill be high from cages. Frequent culling and maintenance of uniform sizedfishes in the cages will ensure uniform growth and high production. Productionof 6-8 kg/m2 is possible, under normal maintenance and 20-25 kg/m2 fromintensive management.7.3.8 Integration of cage culture with shrimp cultureSeabass show addictive nature to selective feed and if they can beweaned to feed on floating pellets, they may not prey upon shrimp asnormally experienced in shrimp culture ponds. By maintaining water deptharound 1.5-2.0 m, cages can be installed in shrimp pond itself and seabassseed weaned to feed on floating pellets can be stocked in the cages andreared.

7. HARVESTING AND MARKETING OF SEABASS8.1 HarvestingSeabass is harvested according to the demand in the market. Thepreferred size is generally around 0.75 to 1.5 kg. The fishes are caughtfrom the culture ponds using dragnets after reducing the water level. It iseasy to harvest fishes from cages and the required size can be selected andharvested in live condition.8.2 MarketingSeabass can be marketed live or dead or in chilled frozen conditiondepending upon market preference and demand. The price varies betweenRs.70-150 per kg.8.2.1 Marketing of l~ve fishMarketing of live seabass is common in South East Asian countriesand it fetches 20-25% higher price than dead fish. For morketing in livecondition the fish should be handled carefully at the time of harvest andtransported to the consumer site without stress or injuries. The harvestedfishes are starved for 24 hrs to prevent excessive fouling of the water duringtransportation due to excretory wastes like ammonia. For transportation todistant places, the water temperature is reduced to 20°C.

8.2.2 Marketing dead fishImmediately after harvest, fishes should be placed in plastic boxeswith crushed ice at 1 :1 ratio on alternate layers for maintenance of qualityand then marketed.8.2.3 Export potentialInternational market for chilled seobass exist in South East Asian countries, especiallySingapore.

CENTRAL INSTITUTE OF BRACKISHWATER AQUACULTURE(India11 Coul~cil ol' Agricult~lral Research)flendquarters1)irectorCcntrul Institute of Brackisl~rvnter A~IIHCLIIIU~~75. Santllonle Higll Road.Ibja Annanlalaipuranl,Cllcnnai - 600 028.lelepl~o~,es : Director (l'ersonal) 236 17523EPABX 246 169482461881724610565230 1 10621'clcyl.arli : Monodo~l1.2s : 0091-044-246 1 03 1 'E-111ailciha@t~i.~lic.inWcbsite : www.icar.org.i1ltc1lr;1l111~l~~.I1t11~Muttukuilu Experimcntnl StationOl'liccr - l~~-Cli:~rgcMultuk~du E~prrin~cntnl Stution of CIS1Knkdwip Research CentreOficcr - In-Cl~argeKnkdwip Hesctlrch Centre of ClBAKilhdwip - 743 337.West Bellgal.li.lcpllollc :I'uri Research CrntreOfficer - In-ChargeI'uri Reseiireh Centre of CIBA15. L3.S. Nagar. Talbania.I'uri - 752 002.Orr~sa.'~eleplione :