Asian Seabass, Lates calcarifer is an economically important marine finfish reared in India. The species is a protandrous hermaphrodite and is known for its differential growth rate. Because of this inherent problem, uniform sizes of Seabass fingerlings are obtained only after careful grading of a sizeable population. Therefore, a farmer has to start with proportionately high numbers of fry in nursery rearing so that he ends up with the required numbers of fingerlings for stocking. Often the yield is a mixture of different size groups.
An experiment was conducted at the Marine Finfish Hatchery of Mandapam Centre for Sustainable Aquaculture to find out the size distribution of Asian Seabass in nursery rearing. Three thousand Seabass fry ranging in size from 3.1 - 2.1 cm with an average size of 2.58 ± 0.276 cm(n=20) were reared in FRP tanks of 2000 L capacity at a stocking density of 3 fry/2 L of seawater. The fry were reared from 18.09.2017 to 28.12.2017 for a period of 102 days. During the rearing period, the water quality parameters like Salinity, Temperature and pH were recorded daily and Dissolved Oxygen done on a weekly basis. Salinity ranged from 32.1 - 34.3 ‰; temperature from 27.1 - 30.7⁰C; pH from 7.5 - 7.6 and Dissolved oxygen from 4.4 to 8.3 mg/L.
They were fed on commercial feed of sizes 500 µ (Crude protein - 48.94 %), 1000 µ (Crude protein - 41.96 %) and 1500 µ(Crude protein - 48.49 %). Uneaten feed and wastes were removed daily by gentle brushing and siphoning through the bottom of the tank. Hundred percentage of seawater was exchanged daily. Manual grading of the Seabass fry was done once in a fortnight so as to avoid cannibalism. At the end of the rearing period, 641 seabass fingerlings survived with the size groups starting from 7.0-7.5 cm till 13.1 - 13.5 cm with a class interval of 5 cm. The modal class of the size distribution of Asian Seabass was found to be in the range of 10.1 to 10.5 cm contributing 18.8 %. The other highest class intervals were found to be in the range of 8.6 - 9.0 cm (12.6 %), 9.1 - 9.5 cm (15.2 %) and 9.6 - 10.0 cm (15.13 %). The population of the seabass was normally distributed. The results obtained in this experiment would be useful to interpret the probable size ranges that may be obtained in nursery rearing of Seabass.