VPP 322: Aquatic Animal Diseases, Health Care and Management (1+1)

INDUCED BREEDING IN LATES CALCARIFER (MARINE FISH) 

 

Image copyrights: Mya Than Tun

• The determination of sex in L. calcarifer, also known as sea bass by external characteristics is almost impossible. For the inducement of this species, wild brood stock are often employed. The matured males are recognized by their distended belly.Females can be identified by sucking out some eggs with a narrow polyester straw for microscopic observation. Healthy and viable eggs are round, pale yellow and float and roll smoothly in seawater of salinity 26-32%. Normally one or a few male fish will give sufficient milt to fully fertilize eggs collected from one female fish. The number of eggs stripped from a mature and gravid female at one time ranges from 2,50,000 to 5,00,000. The fertilization is effected by mixing sperm and eggs together for 5 minutes and the adding clean sea water. The fertilized eggs are transferred to conical fibre glass tanks having a capacity of about 2 tonnes. The eggs hatch out in 12 hours and the newly hatched larvae are transferred to round fibre glass tanks for rearing.
• This species is induced to spawn with HCG especially 2-3 days before full moon. However, the exact and favourable dosages of HCG for inducement are yet to be determined. However, the influence of LHRH (Leutinizing hormone releasing hormone) analogue in the pelleted form (LHRH ehtylamide) or the superactive analogue of mammalian LHRH in the maturation of ovary and acceleration of ovulation in L. calcarifer is well established. The LHRH analogue is incorporated in cholesterol pellets of 2x5 mm and each of such pellets has a strength of 25 or 50 μg of LHRH. The transplantation can be done before 2 months of anticipated spawning period. The pellets are  inserted into the periviceral cavity of selected brood male and female through the ventral body wall. Normally, sutures are not required. Treated female is found to spawn in 2 days with the eggs of measure 0.5 mm.