FINFISH CULTURE SYSTEMS

CULTURE OF MILKFISH The milkfish Chanos chanos - only species of the family Chanidae Does not form a capture fishery significance Important in large scale farming in Southeast Asia Culture originated in Indonesia and spread to the Philippines and Taiwan Marine fish of the Indian and Pacific oceans The young ones spend their life in inshore estuarine areas and ascend rives to the fresh water zones They are highly euryhaline and can live in fresh to hyper-saline waters Tolerate temperature from 15-40oC but the optimum is between 20 and 33oC

Culture systems: Includes nurseries, and rearing ponds Usually- monoculture systems; can also be polycultured with mullets and shrimps The more important farming system in freshwaters - pen farming -in lakes in the Philippines (Laguna de Bay and Lake Sampaloc)

Fry collection: Milkfish don not mature and spawn naturally in captivity Spawn near the coast and larvae occur periodically along the sandy coasts and in the estuaries- collected from wild Gears - different types of dip nets, such as the triangular scissor net in the Philippines and the scoop net in Taiwan Dip nets suited for areas with large concentrations of fry Seine nets, drag nets and traps are

In traditional methods - fry congregating devices -rock walls or lure line made of fibre ropes strung with plaited strips of coconut and banana leaves Power boats are also use to tow seine nets and scoop nets. This extends the area of collection to off the immediate coast and is more efficient. The best collections are made at the creek mouths. The fry accumulated in 2-6m³ shaded concrete tanks near the collection site in about 10 cm of water at a density of about 40,000 fry per tank Fry are then packed in polythene bag filled with water and pure oxygen and deliver to fry dealers Dealers hold the fry in cement tanks before selling to the farmers

Artificial propagation: Since the supply from wild may not be sufficient to supply the demand the AQD of the SEAFDEC in the Philippines has developed technology to produce milkfish in hatcheries Brood fish are reared in captured from the wild and reared for several years in captivity since this fish matures at the age of 5-7 years when it is at least 3.5kg weight and 60 cm in length The fish are induced to spawn implantation of LH-RH cholesterol pellets

Eggs are collected with plankton nets and hatched Fry start feeding in 2 days They are maintained in green water, fed small rotifers and fertilized oyster eggs After 10 days live feed is replaced by commercial artificial feed At a density of 1500 t 6000/m2, two to three weeks after hatching fry reach 1.5cm.

Grow-out Fish ponds: coastal low lands/mudflats The land should between average sea level and 45 cm above sea level The elevation should be such that ponds can be dried completely Soil should be loamy or silty loam. The farm consists of production ponds, wintering ponds, nursery ponds and water canals Production ponds: the area of the production ponds is 3 – 8 ha, their long sides at 90o to prevailing wind Bottom is flat with a drop of 3 cm per 100 m2 Trenches converging at sluice gates should be made at the bottom Water depth should be maintained at 45 cm.

Wintering ponds: Necessary when temperature falls ‹15 °C Comprise 2-5% of the farm area. Nursery ponds: 18 to 25m wide and 20 cm deep along the length of the production ponds. They consist of 2-3% of the farm area. Water canal: Constructed to supply and drain water to and from the ponds. Connected to sluice gates and can be up to 15 m wide

Pond preparation: Decomposing algae are raked and spread evenly Dykes are repaired and all leaks plugged Ponds are dried to get rid of pests and to oxidize pond sediments Fine mesh nets are installed in the inlets to prevent unwanted organisms from entering the ponds Natural food, lab lab is grown at the bottom Apply agricultural lime at 1 ton per ha and chicken manure at 2 tons per ha on moist pond bottom A week later apply ammonium phosphate at 20 kg per ha and urea at 10 kg per ha pond manuring

The amounts of inputs may be changed depending on the productivity and pond history As lab lab grows, increase water depth to 30 cm Fertilizers again added after biweekly water exchange at the same or half the basal rate Fry of about 5 mg size are stocked at the rate of 75 to 100 per m2. They are harvested when they reach 5-10 g Grow out ponds are similarly prepared at stocked with fingerlings of size 5-10g at the rate of 7000-8000 fingerlings per ha

Water management: 30cm water level is maintained for first 30-40 days with lab lab It is increased to 50-100 cm when fish grow bigger and supplemental feeding starts Pumping may be necessary to keep the pond water at a higher level than outside Monitor dissolved oxygen at 6-8 AM and 2-4 PM Aeration becomes necessary if oxygen levels drop to 1 ppm.  

Supplementary feeding: The fish fed are a mixture of rice bran and oil cakes at the rate of 2-3% of the body weight Feeding should be avoided on over cast days and when oxygen levels fall below 2 ppm Harvesting: Over wintered fry of 100 to 150 g reach marketable size of 300 to 450 g in eight weeks New fry reach market size in 5 months After 2 months of stocking fish can be partially harvested by dragging gill nets Final harvest is carried out when all the fry reach marketable size A production of 2000-5000 ka/ha/year can be expected from semi-intensive culture of milkfish