Effects of salinities on growth, survival and digestive enzymes activity of larval hybrid tilapia (Oreochromis niloticusO.aureus)

Influences of salinity on growth, survival and digestive enzymes of larval hybrid tilapia were investigated in the present study. Tilapia at an initial averageweight of 0.0080.001 g were divided into triplicate groups and were observed at salinities of 2, 4, 6, 8, 10 and freshwater 0. The results showed that the effects of different salinities on tilapia growth were significant (P0.05), and larval growth was faster when salinities were 4 and 6 with a growth rate of 0.08 cmd-1 and an absolute growth rate of 0.033 gd-1. When the salinity was 10, the growth of larval tilapia was slower; the growth rate was 0.06 cmd-1 and the absolute growth rate was 0.023 gd-1. Since the conditionfactors of six groups were 3.43~3.81, each groupwas not significantly different (P0.05). Within the salinities of 0~10, the ratio of hybrid tilapia juvenile was 66.0%~67.3% and the survival rate was 92.3%~94.7%; each group did not differ significantly (P0.05). Moreover, the activities of pepsin and trypsin were weakening with increasing salinity, being the highest at salinity of 0, while the activities of lipase and amylase were the highest at salinity of 4 and the lowest at 10. The results suggested that the suitable salinity for larval tilapia was about 4.6.