Introduction to Milkfish Farming in India
Milkfish is one of the most popularly cultured species of fishes in the international and domestic markets. It is consumed either fresh or processed. Milkfish is the only species in the Chanidae family. Milkfish only spawn in fully saline waters.
A Step by Step Guide to Milkfish Farming in India
Milkfish can live in both seawater and freshwater but the only breed in pure seawater. This means they will not breed in a pond or a lake, like a tilapia. If you want to grow Milkfish in a pond you will have to catch babies from the sea to put into the pond.
Site selection for Milkfish farming
Milkfish farming can be started in any existing developed and operational brackish water fish farms. The site should have a minimum water depth of 0.8 to 1 meter; good quality of water with optimal Salinity of 10 to 30 ppt, Temperature of 20 to 30°C, Water pH value of 7.5 to 8.5, Dissolved Oxygen (DO) of 4.0 to 5.0 ppm around the year. Milkfish can be grown in freshwater and tolerates low levels of DO and high levels of Ammonia compared to other cultivable fish species. Pond soil should be sandy or silty clay loam. Good access to roads from the farm site and the power supply is also necessary for Milkfish farming site to reach markets for easy culture operation
Site selection, considering both the technical and non-technical aspects, is a requirement for hatchery operation. A major technical criterion in selecting a site for a Milkfish hatchery is as follows;
- The area must be flood and pollution-free and should be near the water source
- Adequate good quality sea and freshwater should be available the whole year round
- The area should be near the broodstock source the non-technical criteria include access to transportation (for the transport of broodstock and fry); supply facilities like feeds, fertilizer, chemicals, etc.; and labor support.
Seed Collection for Milkfish
Milkfish does not mature and breed in culture ponds and confined waters; the development of a hatchery technology has been difficult. Though induced breeding has been successfully carried out in this species, the final survival rate has been less and hatchery operations hence are not economical. In this respect, the most suitable method is the collection of seeds from natural sources. In India, the seeds of Milkfish measuring 2 to 7 cm in length occur along the coast of Orissa, Tamil Nadu, Andhra Pradesh, Kerala, and Karnataka. Milkfish seeds need clear calm inshore waters of gently sloping beaches including tidal creeks, estuaries, brackish water bodies, and mudflat areas where the temperature is about 23 to 25°C and salinity varies between 10 and 32 ppt.
The Milkfish seeds are collected from low-lying areas using scoop nets, dip nets and hand nets. Soon after collecting the seeds are conditioned by keeping in a limited volume of clear water for a definite period without food. Seeds are transported in containers with diluted seawater of 10 to 15 ppt salinity.
Water Supply and Hatchery Production for Milkfish
Water supply is the most important factor to consider in the suitability of a fishpond site. Generally, the water supply comes from a river, sea, or creek. It must meet the quality and quantity of the pond requirements throughout the year. It would be futile to develop a site if the source of water is polluted and the volume is inadequate.
Milkfish hatcheries contain larval rearing tanks, culture tanks for rotifers and green algae and hatching tanks for brine shrimp. Larval rearing may be either operated in indoor or outdoor systems, depending on the specific conditions in the countries where fry is being produced.
Hatchery operations utilize either semi-intensive (low stocking density, minimal water exchange, high volume tanks, feeding with mixed diet) or intensive (high stocking density, high volume tanks, daily feeding and water exchange) systems, with an average survival rate of 30% (from stocked newly-hatched larvae). After hatching, the larvae are ideally kept at 50/liter in hatchery tanks (either fiberglass, concrete, canvas, or polypropylene-covered earthen tanks) maintained with Chlorella and fed with rotifers during the early stages and later with brine shrimp for a total of 3 to 4 weeks. Following this, their size ranges between 2 to 3 cm and they are ready for transport to nurseries. Then, the fry may change hands two or more times before being used for grow-out; each time this happens, they are sorted and counted, transported, and stored for different periods. Fry is an extremely perishable commodity and some of them die during the gathering, transport, storage, nursery rearing, and grow-out. The technologies for fry transport and storage are generally effective, although perhaps not yet optimized. Fry are stored in a cool place in plastic basins or clay pots at 100 to 500/liter, in the water of 10 to 25%, which is renewed daily. Dealers may store fry for 1 to 7 days, depending on the demand. Fry can be maintained on wheat flour or cooked chicken egg yolk for 1 to 2 weeks but soon begin to die, despite continued feeding. Recently, micro-encapsulated feeds have become commercially obtainable for finfish but the cost compared to conventional live feeds is higher.
Nursery Rearing of Milkfish
Nurseries are ponds for rearing the fry until they attain 5 to 7 cm in length. The area of nursery ponds ranges from 500 to 5,000 square meters. At the nursery site, the fry is acclimatized to the salinity of the pond water. The preparation of the pond for stocking with fry has to be started about 1 or 2 months in advance. The ponds are drained and dried for around 10 to 15 days and later tilled and raked. Lime is added at 1000 kg/ha and freshwater is let in. Pond water is fertilized with inorganic and organic fertilizers. Once the algal bloom develops more saline water is added to a height of 10 cm. Within 3 to 7 days, a complex of blue-green algae, bacteria, diatom, nematode worms develop at the bottom of the pond and it is called “Lab-Lab”. This algal consortium is most vital for developing fries of Milkfish. Stocking to the nursery pond is generally done only after “Lab-Lab” has developed in the pond. The fry is stocked at densities of 20 to 50/ m2. The threat of predatory fishes, snakes, and crabs can be screened from entering the pond using nets. Establishing poles along the embankments and crisscrossing with strings can discourage predatory birds. One serious cause of mortality of seeds in fry ponds is the sudden reduction of salinity and temperature due to heavy rains. Filling the ponds with brackish water before rains, it may prevent such an eventuality.
The fry feeds actively on Lab-Lab and phytoplankton and grows rapidly. By the end of one month, they measure 5 to 8 cm long and weigh 1.5 to 5 gm, when they are ready for transfer to the production pond or pen structures for rearing. They are captured by partly draining the fry ponds at low tides when the fry generally congregates near the water gates, for which seine nets are used.
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Growing Techniques for Milkfish Production
Milkfish may be on grown in ponds, cages or pens.
Pond Culture of Milkfish
The culture of Milkfish in ponds may be in deep-water or shallow systems. Milkfish are usually cultured in shallow brackish water ponds in which the growth of benthic algae is encouraged through organic or inorganic fertilization. This will survive on benthic algae alone if the productivity of the algae more than the grazing rate of the fish; or else, supplemental commercial feeds are applied.
Shallow water pond design generally consists of many nursery and production ponds with a typical area of 2000m² for nursery ponds and 4 hectares for production (on growing) ponds. Naturally, ponds have a depth of 30 to 40 cm and are provided with independent water supplies.
The average yield of an integrated nursery, transition, and shallow grow-out system that produces 3 crops a year is 800 kg/ha. Modified modular pond designs containing a series of grow-out compartments with a maximum of about 8 crops a year have been shown to increase yield to a high as 2,000 kg/ha.
Deep-water ponds offer a more stable environment and extend the grow-out period into the winter season. Most deep-water Milkfish ponds have been created by converting either freshwater ponds or shallow water ponds, with a depth of 2 to 3 meters.
Pen Culture of Milkfish
As the main production of the lake cannot meet this sudden expansion of aquaculture, and feeding became essential to meet the cultured fish nutritional requirements. Pen operators stock fingerlings at 30,000 to 35,000/hectare and provide supplemental commercial diets. However, the disease spreads among culture pens and causes mass mortality. Government regulations are now considered to maintain sustainable yields from this type of farming.
- In pen, Milkfish fingerlings of 40 to 60 g body weight can be stocked with a stocking density of 30,000 to 40,000 nos./ ha once or twice in a year depending upon the water quality and growth performance of the fishes and facilitate the partial harvesting of bigger sized fishes.
- Milkfish fingerling feeds on naturally available lab-lab in the low stocking density pen culture system.
- 10 to 20 tonnes/ha of Milkfish can be harvested by using the supplemental feed in high stocking density pen culture grow out system.
Cage Culture of Milkfish
Fish cages are smaller in size and more restricted enclosures that can be staked in shallow waters or set-up in deep water with appropriate floats and anchors. Cage farming of Milkfish is usually carried out in marine waters along coastal bays. Stocking rates are quite high, it would be 5 to 30/m³.
- Small cages can be staked in shallow waters depth up to 2 meters along the coastal bays or set-up in sea-based deeper water with appropriate floats and anchors for Milkfish culture.
- Fingerlings of 40 to 60 g body weight are reared in net cages with a stocking density of 5 to 30 fingerlings/ m³.
- Specially formulated floating or semi-sinking pellet feed can be supplied to the fishes by 3 to 5% of the bodyweight daily basis
- Depending on the water quality, Milkfish yield in cage culture could be 10 to 20 kg/m3
Feeding Practices for Milkfish Production
Milkfish feed supplies are manufactured commercially in the form of starters, growers, and finishers, which are administered according to the Milkfish production stage.
Milkfish is considered as a herbivorous fish. Artificial or formulated feed in the form of slow sinking or floating pellets can be provided during culture operation. Feeding efficiency can be improved by providing pellets for feeding. Pellet, having a diameter of 4 to 5 mm and length of 6 to 8 mm is suitable for Milkfish of more than 100g body size. Crude protein requirement of fry, fingerling, adult, and brood Milkfish is 40%, 36%, 24 to 28%, and 36% respectively.
What Protein Level Should Use for Milkfish Diets?
A suitable Milkfish diet will have the following crude protein levels under semi-intensive and intensive farming conditions – fry 40 to 46%, fingerling 25 to 40%, juvenile 25 to 40%, and broodstock 36%.
Disease in Milkfish Farming
Milkfish is a hardy species. The prevalence of the disease in the Milkfish grow out system is less compared to other cultured finfish species. High stocking density may lead to parasitic infections. Wild seeds suffer from parasitic infections. Rough handling and stress induce deformities and mortalities due to bacterial infection during Milkfish farming.
Harvesting Techniques of Milkfish and Yield
Milkfish are normally harvested at sizes of 20 to 40 cm. There are 3 known methods used for harvesting Milkfish:
Partial harvest – Partial harvest technique is the harvest of uniformly grown Milkfish from grow-out facilities by using gillnets, retaining the undersize fish with an average body weight of 250 g or larger.
Total harvest – Total harvest is the Complete/whole harvest in one crop period from grow-out facilities (i.e. total draining of ponds by pump or gravity or, hauling off the entire net cage structure, seining or the use of gillnets in pens). The harvest size at this stage may vary from 250 to 500 grams.
Forced harvest – Forced harvest is an Emergency harvesting, irrespective of fish size or grow-out stage, which is carried out during ‘fish kills’ because of oxygen depletion that is attributed to algal blooms, red tide occurrence, pollution, and other environmental causes.
Milkfish has a higher growth rate in its first year in brackish water when it grows to a marketable size of 30 to 45 cm long and 300 to 800 grams in weight. The periodicity of harvesting mainly depends upon the number of batches stocked. At the time of harvesting the pond is drained using pumps, while in the case of pens, the lowest tidal period is the best time for harvest. If in case trenches were provided in culture ponds, it is easier to gather all the fish inside the trenches by draining the water and then capturing them. Generally, seine nets are operated for capturing farmed fish. The survival rates range from 80 to 95% amounting to a production ranging from 500 to 1000 kg/ha in ponds and 250 to 500 kg/ha in pens.
Extensive Milkfish ponds typically produce a gross yield of 500 to 750 kg/ha/crop. Some farms may achieve gross yields approaching 1000kg/ha/crop.
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