CULTURE OF GREY MULLETS

Grey mullets and milkfish are one of the important group of cultured species in Vallis of the Mediterranean lagoons (Italy) Coastal harbour culture' of China Gangetic and Southern estuaries of India Coastal fish ponds of Hawaii The striped mullet Mugil cephalus -widely distributed -larger size and faster growth rate Eurythermal and highly euryhaline; tolerating salinities between 0 and 75 ppt Feeds on detritus, large plants, blue green algae, green algae and diatoms Valued not only for meat but also for roe which is a delicacy in Taiwan and Japan

Culture systems The traditional and extensive culture with other euryhaline species They are generally raised with other species in polyculture- In Hong Kong with Chinese carps In Taiwan with Chinese carps and Tilapias In Israel with common carp and tilapias In India with shrimps, pearlspot and other fish in traditional prawn culture systems In the Philippines and Indonesia with milkfish.

Fry collection fry obtained from natural systems Striped mullet breeds in the sea, fry and fingerlings enter estuaries and congregate in shoals Fry collection -seines and dip nets are used Most suitable areas for collection are marginal areas of rivers, tidal streams, creeks, swamps and inundated fields. They swim against slow currents and such areas are ideal sites for collection

Hatchery production 1 st in Taiwan -artificial propagation of stripped mullet 2.5 to 3 years old spawners are obtained from the sea and stocked in cement tanks They are injected with 3-5 mullet pituitary glands mixed with rabbit units of synahorin (mixture of chorionic gonadotropin and mammalian hypophyseal extract) per female or with salmon gonadotropin Eggs with best chances of fertilization are released hours after hormone injection A soft swollen belly with excretion of calcium deposits indicates they are ready to release eggs

Females are stripped and eggs are mixed with milt collected from males Both dry and wet fertilization can be followed. 1.0 to 1.5 million eggs can be obtained per female Eggs are incubated in flow through systems are in aquaria with static water and aeration Eggs hatch in 34 to 48 hours at a temperature of 24°C. Larvae are reared in indoor tanks Newly hatched larvae are planktonic, they swim with heads down and bellies up Larvae start feeding three days after hatching. They are fed fertilized oyster eggs. From 5 th day onwards they are fed with rotifers and copepods In 45 days fry are ready for stocking in grow-out ponds.

Grow-out operations Tidal stocking - quantity and composition of stock can seldom be determined The aquaculturists – wild caught Traditional culture system - Regular water exchange, Natural food enters along with the tidal water on which mullets and other fish feed They also feed on benthic algal mat growing in the ponds Production in this system varies from 150 – 1500 kg/ha

In Hong Kong – 10,000 to 15,000 fingerlings of 7.5 cm long along with 1000 to 2000 Chinese carps per ha – Thinned out 3500 per ha when the fish grow to 12 cm size – Feed - rice bran for the first two months and thereafter a mixture of rice bran and oil cake – Production varies between 2500 to 3500 kg/ha/year. In Taiwan – stocking mullet fingerlings, 2000 milkfish, 3250 Chinese carps and 500 common carp – fertilized with 60 kg/ha – Feed - mixture of rice bran, soya bean cake and peanut meal – Striped mullet -300g in one year and 1.2Kg in the second year – 3 year old -2 Kg under pond conditions