Effects of low-salinity on growth, body composition, plasma osmolatity and gill Na + -K + -ATPase activity of juvenile orange-spotted grouper, Epinephelus coioides

Effects of salinities (3‰, 5‰, 8‰, 12‰, 15‰ and 31‰) on growth, body composition, plasma osmolalitity and gill Na + -K + -ATPase activity of juvenile E. coioides (initial weight 44.17±0.19 g) were investigated by an 8-week trial. Results showed that fish reared at 3 ‰ and 5 ‰ had lower survival than fish reared at other salinities (P<0.05). Fish reared at 12 ‰ had the highest weight gain (WG), length gain (LG) and specific growth rate (SGR), while fish reared at 3 ‰ had the lowest. Fish reared at 31 ‰ had the highest condition factor (CF), while fish reared at 3 ‰ had the highest hepatosomatic index (HIS). Body crude protein and ash content were not affected by salinity, while crude lipid and moisture increased significantly with the increase of salinity. Body energy of groupers cultured at 12 ‰ salinity was the highest. The plasma osmolality showed a clear and significant negative linear relationship with salinity (Y=- 2.3564X+426.73, R 2 =0.9121), and with external osmolality (Y=-0.0923X+430.68, R 2 =0.9483). Fish reared at 3‰ had the highest gill Na + -K + -ATPase activity, while fish reared at 12‰ and 15‰ had the lowest. The reduced gill Na + -K + -ATPase activity found at 12‰ may lead to reduced energy expenditures thereby contributing to higher growth rates. These results suggest that E. coioides have a very strong ability of osmoregulation. E. coioides could be well cultured at low salinity, and the optimal salinity was 12‰. Our findings may have implications for E. coioides farming expanded into new areas such as inland saline water.