Effects of pH on survival activity index and growth of larvae of hybrid tilapia (Oreochromis niloticusO.aureus)

Influences of pH values on larval activity index (SAI) and growth of hybrid tilapia (Oreochromis niloticusO. aureus) were investigated in the present study. The SAI and growth of newly hatched larvae of hybrid tilapias were observed at pH values of 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5 and 9.0, with water temperature at 280.5℃. Larval tilapias were at an initial average size of 0.0080.006 g. The experiments lasted for 28 days. The results showed that SAI was correlated to pH in a conic form, with R2=0.9313 (P0.01); when pH values were 7.0 and 7.5, SAI values were 33.30 and 32.85 respectively; when pH values were 9.0 and 5.5, SAI were 18.98 and 20.04 respectively. pH values were 5.5~9.0, the growth rate was 0.048~0.055 cmd-1 and the absolute growth rate was 0.013~0.014 gd-1, larval tilapia growth did not differ significantly (P0.05). Under pH values between 7.5 and 7.0, the survival rates were 89.3% and 87.0%. The present study suggested that suitable pH range for the survival of larval hybrid tilapia was 6.0~8.5 and that for the growth of larvae was 7.0~7.5.