Culture Technology for Lates calcarifer

Khaimesh Sehgal* and Girija Phadke

*Central Institute of Fisheries Education, Seven Bunglows, Versova, Andheri (W.), Mumbai, Maharashtra, India 400061.

Corresponding Author: sehgal.cife@gmail.com

Introduction:

Brackish water fish culture is still in the early stages of development in India. The present practices are based on the availability of natural fry and often several species are either purposely stocked or they gain entry with the tidal water, in spite of preventive measures.

Important Species:

The more common species in brackish water ponds are mullets, tilapia, catfish and sea bass. The combination of species is only incidental and not actually based on their compatibility in terms of the use of food available or other habits. In so far as tilapia are concerned, the problem of prolific breeding, over-population and stunted growth occurs at least when all available species gain entry. Mullet fry are generally available in required numbers, but the growth and production achieved so far are not high. This is largely due to the nature of the soil on which brackish water ponds are built. Coastal swamps and mangrove areas used for pond construction generally have peaty acidic soils. Besides the difficulties of building watertight dikes with peaty soils, serious problems of maintaining favourable pH of water and soil for the growth of benthic as well as planktonic fish food organisms are faced during the first few years of pond operation. Till the toxic salts are leached out from the soil and its texture improved by the deposition of silt brought in by high tides, which may take as much as two or three years, the growth of adequate quantities of natural food can't be relied upon for high density culture of mullets or other fish.

 

Culture technology for Seabass:

Seabass has been commercially cultivated in brackish water and freshwater ponds and marine cages in many Southeast Asian countries. While the cage culture technology is now established, grow-out techniques in pond are still are still in the developmental stages.

The major problems that are always encountered during culture period are cannibalism during young stage (1-20 g) and dependence on trash fish as a main diet which has a very limited supply. Despite some imperfections, the basic techniques of seabass culture are now developed and have been considered economically viable.

Systematics:

Phylum: Chordata

Sub-phylum: Vertebrata

Class: Pisces

Sub-class: Teleostomii

Order: Percomorphi

Family: Centropomidae

Genus: Lates

Species: calcarifer

Life history:

Seabass spends most of its growing period (2-3 years) in freshwater bodies such as rivers and lakes, which are connected to the sea. It has a rapid growth rate, often attaining a size of 3-5 kg within 2-3 years. Adult fish (3-4 years) migrate towards the mouth of the river from inland waters into the sea where the salinity ranges between 30-32 ppt for gonadal maturation and subsequent spawning. The fish spawns according to the lunar cycle (usually at the onset of the new moon or the full moon) during late evening (1800-2000 hours) usually in synchrony with the incoming tide. This allows the eggs and the hatchlings to drift into estuaries. Here, larval development takes place after which they migrate further upstream to grow. At present, it is not known whether the spent fish migrates upstream or spends the rest of its life in the marine environment

Smith (1965) noted that some fish spend their whole life in freshwater environment where they grow to a length of 65 cm and 19.8 kg body weight. The gonads of such fish are usually undeveloped. In the marine environment, seabass attaining a length of 1.7 m have been recorded in the Indo-Australian region.

Fig: Migration pattern of Lates calcarifer

Feeding habits:

Although the adult seabass is regarded as a voracious carnivore, juveniles are omnivores. Analysis of stomach content of wild specimens (1-10 cm) show that about 20% consists plankton, primarily diatom and algae and the rest are made up to small shrimp, fish, etc. Fish of more than 20 cm, the stomach content consists of 100% animal prey: 70% crustaceans (such as shrimp and small crab) and 30% small fishes. The fish species found in the guts at this stage are mainly slip mouths or pony fish (Leiognatus sp.) and mullets (Mugil sp).

Sex determination:

Identification of the sexes is difficult except during the spawning season. There are some dimorphic characters that are indicative of sex:

+      Snout of the make fish can be slightly curved while that of the female is straight.

+      The male has a more slender body than the female.

+      Weight of the female is heavier than males of the same size.

+      The scales near the cloaca of the males are thicker than the female during the spawning season.

+      During the spawning season, abdomen of the female is relatively more bulging than the males.

Sexual maturity:

In the early life stages (1.5-2.5 kg body weight), majority of the seabass appear to be male but when they attain a body weight of 4-6 kg majority become female. After culture period of 3-4 years, however, in the same age group of seabass both sexes can be found and identified as mentioned above. In a fully mature female, the diameter of the oocysts usually ranges from 0.4 to 0.5 mm.

Culture techniques:

As mentioned above, cannibalism is one of the most serious problems in seabass culture. High mortality is often encountered when uneven sizes of the fish are stocked. This has been noted to occur mostly where the fish are very young (1-20 cm in length, the first two months of culture). To minimize this problem, culture of seabass should be approached in two phases i.e. the nursery phase and the grow-out phase.

A) Nursery Culture:

The main purpose of the nursery is to culture the fry from hatchery (1-2.5 cm in size) to juvenile size (8-10 cm). This can solve the problem of space competition in the nursery tanks. Beyond the nursing period, the juveniles can be graded into different size groups and stocked in separate grow-out ponds. It has been observed that the juveniles from the nurseries perform better in terms of growth and survival than those stocked directly into the grow-out ponds.

Nursing the fry in concrete tanks is not recommended, as accumulation of excess feed on the bottom of the tank cannot be avoided. Such accumulation can cause bacterial disease. In addition, constant contact with the tank wall results in wounded fish and subsequent bacterial infection

a) Nursery pond design:

Nursery pond size ranges from 500 to 2000 m² with water depth of 50-80 cm. The pond has separate inlet and outlet gates to facilitate water exchange. Pond bottom should be flat and sloping towards the harvesting or drainage gate. Inlet and outlet gates are provided with a fine screen (1 mm mesh size) to prevent predators and competitors from entering and fry from escaping the pond.

Fry ranging from 1-2.5 cm are suitable for stocking in the nursery ponds. Stocking density is between 20-50 individuals per square meter.

b) Pond preparation:

A well-prepared pond is important as predators and competitors can endanger the stocked fry. Some farmers still practice very crude farming techniques of drying the pond bottom and immediately filling with water and stocking fry directly for nursing. Feeding is entirely dependent on supplementary feed such as chopped or grounded trash fish and is done twice daily in the morning (1800 hours) and afternoon (1700 hours). In this method, the survival rate and growth rate are low.

To enhance production, the following improved pond preparation techniques are done: The nursery pond must be drained and dried until the bottom soil cracks to release toxic gases, oxidize mineralized nutrients, and eradicate some pests and predators. In cases where the pond cannot be completely drained, derris root (rotenone) may be applied at the rate of 20 kg/ha to eradicate unwanted species. Derris root is prepared by cutting them into small pieces, crushing and soaking in water overnight. Only the solution is applied to the pond. If derris root is not available, a mixture of 50 kg/ha of ammonium sulfate (21-0-0) with lime at a ratio of 1:50 will be sufficient to weed out unwanted species. The mixture is applied to the portions of pond with water. The use of any chemicals or inorganic pesticides is not recommended because the residual effect remains for many years and can reduce the pond production. If pond soil is acidic, the pond bottom should be neutralized with lime before letting the water in.

The improved technique is based on the live food production in the pond supplemented with chopped or grounded trash fish. After neutralizing pond bottom by liming, organic fertilizer (chicken manure) is applied at the rate of 500 kg/ha. Then water depth is gradually increased for the propagation of natural food. Two to three weeks prior to stocking, newly hatched Artemia nauplii are inoculated into the pond (1 kg of dry cyst/ha). Artemia will utilize the natural food as feed for growth and will reach adult stage within 10-14 days. The fry are immediately stocked at the rate of 20-50 individual per square meter.

Another approach to the improved technique is to stock Artemia nauplii in the separate pond and grows them into adult. Adults could be harvested daily to feed the fry.

c) Nursery pond management:

Although seabass can be cultured in either freshwater or saltwater, fry must be acclimatized to the salinity and temperature prevailing in the pond on stocking to prevent loss.

Acclimatization is done in the following manner: Transfer the fry to a tank, and then gradually add nursery pond water. This can be completed within one day or more depending on the salinity difference. If the temperature and salinity in transport bag does not differ by more than 5¡C and 5 ppt with the pond water, floating the bag in the pond for sometime to even out temperature difference can do acclimation. Pond water is then added gradually until both salinity become equal and the fry can be released.

Seabass fry are stocked in the nursery pond at a density of 20-50 fry/m². Stocking is usually done in the early morning (0600-0900 hours) or early evening (2000-2200 hours) when the temperature is cooler.

Water replenishment is needed to prevent deterioration of pond water quality due to the decomposition of uneaten feed or excess growth of natural food. Normally, 30% of pond water is changed daily.

d) Feeding:

Supplementary feed is given daily. The feed used for nursing seabass is chopped and grounded (4-6 mm³) trash fish, normally at the rate of 100% of biomass given twice daily in the first week (at 0900-1700 hours), gradually reduced to 60% for the second week and 40% in the third week. This has been found to be most effective feeding strategy for ponds without artemia inoculation.

The application of supplementary feed is a vital operational activity that should be done properly, if not, contamination of culture water and wastage of feeds result. Although the seabass in nature prefer live food, the fish can be trained to feed on dead animal. Prior to feeding, the fish should be attracted by sound (such as tapping a bamboo pole in the water) to induce them to form a school. Feeding time and place should be fixed. After the fish have formed a school, small amounts of feed are introduced by spreading into the water within the school of fish fry. It must be remembered that seabass never eat the feed when it sinks to the pond bottom. Therefore, feeding should be slow. When the fish are filled to satiation, they disappear thus feeding should be stopped. The same procedure should be followed at every feeding time. The first few days after stocking, feeding should be 5 to 6 times a day to teach them to accept dead feed. Once the fish is accustomed to it, which takes about 5-7 days, feeding frequency is reduced to twice daily. In nurseries where Artemia is the main diet, once the Artemia population has thinned down, chopped or grounded trash fish can be supplemented using above described practice.

The nursing period lasts about 30-45 days until fingerling stage (size 5-10 cm). At this stage, they are ready for transfer to grow-out ponds.

B) Grow-out culture:

The grow-out phase involves the rearing of the seabass from juvenile to marketable size. Marketable size requirement of seabass vary country to country e.g. Malaysia, Thailand, Hong Kong and Singapore. The normally accepted marketable size of seabass among these countries and region is between 700-1200 g while in the Philippines, marketable size is between 300-400 g. The culture period in grow-out phase also vary from 3-4 months (to produce 300-400) to 8-12 months.

Feeds and feeding:

Feed is the major constraint confronting the seabass culture industry. At present, trash fish is the only known feedstuff used in seabass culture. Chopped trash fish are given twice daily in the morning at 0800 hours and afternoon at 1700 hours at the overall rate of 10% of total biomass in the first two months of culture. After two months, feeding is reduced to once daily and given in the afternoon at the rate of 5% of the total biomass. Food should be given only when the fish swim near the surface to eat.

Since the supply of trash fish is insufficient and expensive in some countries, mixing rice bran or broken rice to the trash fish minimizes its use.

A very recent development on improving the dietary intake of seabass is the introduction of moist feed.

C) Pond culture:

Although methods of pond culture of seabass have been practiced for over 20 years in Southeast Asia and Australia, not much has been done on the commercial scale. At present, culture of seabass in brackish water pond has been identified in some countries as having tremendous market potential and high profitability. These, however, can be achieved if conditions are met such as adequate fry supply, availability of suitable site and properly designed fish farm. Supply of fry from the wild is very limited. As with cage culture, it is one of the constraints in the intensification of seabass culture in ponds. However, with the success in artificial propagation of seabass, fry supply may largely come from this source in the future. A comparison of hatchery bred and wild fry cultured in ponds did not show very significant difference in growth rate.

There are two culture systems employed in pond culture of seabass:

(a) Monoculture:

Monoculture is that type of culture where a single species of animal is produced, e.g. seabass. This culture system has a disadvantage. It is entirely dependent on supplementary feeding. The use of supplementary feed reduces profit to the minimal, especially where the supply of fresh fish is limited and high priced.

Table 1: Combination of feedstuff

Ingredient Percentage Trash fish 70 Rice bran or broken rice 30

 

Table 2: Combination of moist diet

Ingredient Percentage Fish meal 35 Rice bran 20 Soy bean meal 15 Corn meal 10 Leaf meal  3 Squid Oil (or fish oil)  7 Starch  8 Vitamin mix  2

 

Stocking density:

Fingerlings are stocked at stocking density of 16 no./m².

(b) Polyculture:

This type of culture approach shows great promise in reducing if not totally eliminating the farmers' dependence on trash fish as food source. The method is achieved by simply incorporating a species of forage fish with the main species in the pond. The choice of forage fish will depend on its ability to reproduce continuously in quantity sufficient to sustain the growth of seabass throughout the culture period. The forage fish must be such a species that could make use of natural food produced in the pond and does not compete with the main species in terms of feeding habit such as Oreochromis mossambicus, Oreochromis niloticus etc.

Criteria in the selection of site for seabass culture:

1) Water supply:

The site should have enough good water quality supply all year round. Water quality includes all physico-chemical and microbiological characteristics of water being used for culture of seabass. The following are the parameters normally considered as suitable water supply:

 

2) Tidal fluctuation:

Area best suited for seabass should have moderate tide fluctuation range between 2-3 meters. With this tidal characteristic even for ponds as deep as 1.5 meters, complete drainage during low tide can be done. In addition, the pond can readily admit water during spring tide.

3) Topography:

It is advantageous if the selected site is mapped topographically. This would reduce development and operational costs such as for water pumping.

4) Soil:

Ideally, the soil at the proposed site should have enough clay content to ensure that the pond can hold water. Area with acid sulphate soil should be avoided. Best soil 30%-40% of clay would give good result.

5) Accessibility:

Accessibility is an important consideration in site selection for logical reasons. Overhead cost and delay in the transport of material and product may be minimized with good site accessibility.

Other factors in the selection of site that should be considered include availability of seed, labour, technical assistance, market demand and suitable social condition.

Pond design and construction:

Seabass ponds are generally rectangular in shape with size ranging from 2000 m² to 2 hectares and depth of 1.2 to 1.5 meters. Each pond has separate inlet and outlet gate to facilitate water exchange. The pond bottom is entirely flat leveling toward the drainage gate

Pond preparation:

Preparation of grow-out ponds is similar to the procedure followed in pond system. In monoculture, the fish are stocked immediately after neutralizing the pond soil with lime. Ponds are filled immediately after pond preparation.

In polyculture, after the pond soil is neutralized, organic fertilizer (chicken manure) is applied at the rate of 1 ton per hectare. Then water depth is gradually increased for propagation of natural food. When abundance of natural food is observed, selected tilapia brood stocks are released to the pond at the rate of 5,000-10,000 per hectare. Sex ratio of male to female is 1:3. The tilapia is reared in pond for 1 to 2 months or until tilapia fry appear in sufficient number. Seabass juveniles are then stocked.

Seabass juveniles (8-10 cm in size) from nursery are stocked in the grow-out pond at the rate of 10,000-20,000 per hectare in monoculture and 3,000-5,000 per hectare in polyculture system. Prior to stocking, juveniles are acclimatized to pond culture and salinity conditions. Stocking the fish in uniform sizes will be most ideal and should be done at cooler times of the day.

Lay Out Of Pond:

A preliminary layout of pond can be made after the general topographical map of the area is prepared taking advantage of the existing creek .In making the lay out plan care should be taken to see that as far as possible the requirement of earth for the embankment and filling up low areas can be made out of excavated material. Another factor to be considered in case the ground level is already sufficiently low is the availability of suitable of borrow pit for the construction of embankment. The optimum size of the pond and its ancillaries, the geometrical shape of the pond from economical and management point o view have to be determined for a particular area depending on cost of development and availability of manpower.

These points should be kept in mind while construction a pond:

1. Permissible low water level to be maintained in the pond

2. The required amount of sea and fresh water can be introduced or discharge when ever requirement within permissible period of time

3. Adequate volume of water can be produced in the pond

4. Mixing and diffuse of water may be made efficiently.

5. Requirement of these criteria:

1. A suitable physical environment
2. A suitable economic environment
3. An equitable regulatory environment
4. Incentives
5. Land
6. Water
7. Capital
8. Labour
9. Seed
10. Feed and fertilizer
11. Trained personal

 

Fertilization:

Initial manuring can be done with organic manure @ 20% of the total requirement. It is done 15 days before the stoking. The remaining 80% manure is done in split doses of rearing. Cow dung is spread at @ 2000kg per ha.

Pond management:

Due to the need of maintaining natural food in ponds, water replenishment in polyculture system should be minimized. Water change should be done once in three days for about 50% of capacity.

However, in monoculture where supplemental feed is given daily, there are chances that excess feed may pollute the water. Hence, daily water replenishment is necessary.

 

Source: Google search

[A conventional pond system with Catching pond (CP), Nursery pond (NP), Transition pond (TP), Feed pond (FP) and Rearing pond (RP)]

Fig: Pond Layout for Seabass Culture

Feeds and feeding:

Supplementary feed is not required in the polyculture system, but in monoculture, daily feeding is a normal practice. The method of supplying feed in ponds follows often the practice employed in cage culture.

Production:

Average production of sea bass in brackish water is 2000 Kg/ha.

 

CALENDER OF OPERATION

 

Marketing:

Different market intermediaries namely commission agents, wholesalers, retailers and vendors are operating in fish marketing. When market intermediaries are more the price spread is high. In case of sea bass, fish marketing going through producers to wholesaler to retailers to vendor to consumer.

 

Credit Requirement:

Credit is one of the important inputs required for the promotion of brackish water aquaculture. State co-operative bank, state land develops banks and regional rural banks extend credit for development of brackish water fisheries. The NABARD provides refinance to these banks for technically and economically viable scheme. Banks gives credits for the following investments for brackish water projects, which are refinanced by NABARD.

 

Constraints:

1.     Absence of proper land leasing policies at states level lack of proper institutional arrangement for the sustained supply of seed

2.     Lack of extension support from the state level

3.     Brackish water fish culture needs a lot of investment

References:

Natarajan, M.V., 1987. Brackish Water Fisheries Development in Tamil Nadu, Srivastava,             U.K., Dholakia, B.H. and Vathsala, S. (Eds.) In: Brackish Water Aquaculture             Development in India, CPC, New Delhi, p:21.

Pickett, D.G. and Pawson, G.M., 1994. Sea Bass Biology, exploitation and conservation,             Chapman & Hall, London.

George, A.I. and Sebastian, M.J. Review of the backwater fisheries and brackish water fish      culture in Kerala State, Pillay, T.V.R, (Eds.) In: Coastal Aquaculture in the Indo-            Pacific Region, FAO of the United Nation. p:117.

Rimmer, A.M. and Russell, J.D. (1998) Aspects of the Biology and Culture of Lates             calcarifer, De Silva, S.S. (Eds.) In: Tropical Mariculture, Academic Press, London.             p:450.