Effects of salinity on growth performance, physiological response, and body biochemical composition of juvenile ivory shell (Babylonia areolata)

Salinity change caused by extreme weather is an environmental factor that affects the growth and survival of ivory shell Babylonia areolate. In the present study, the effects of different salinities (20, 25, 30, 35, and 40 ppt) on growth performance, tissue damage, stress-related enzymes and body composition of ivory shells were investigated after seven weeks of salinity adaptation. The results showed that juvenile ivory shells had higher specific growth (SGRBW) and survival rates in the 20-, 25-and 30-ppt groups than those cultured at higher salinity (35 and 40 ppt) (P < 0.05). The width of the gill lamellae first increased and then decreased in response to increasing salinity. Furthermore, obvious tissue damage, such as cytoplasmic vacuolation of gill lamellae and abscission of epithelial cells, was observed in the gills of the hypersaline-stressed groups (35 and 40 ppt). The activities of Na+/K+-ATPase, catalase, and superoxide dismutase, and the contents of malondialdehyde in both the gill and hepatopancreas first decreased and then increased with increasing salinity, and the lowest values were observed at salinities of 25 or 30 ppt. The highest alanine transaminase and aspartate transaminase ac-tivities of the gills were observed in the 35-ppt group, while in the hepatopancreas, their values peaked in the 40-ppt group. The activities of acid phosphatase in both the hepatopancreas and gill showed an increasing and then decreasing tendency, while the alkaline phosphatase activity showed a decreasing tendency in response to increasing salinity. As for the amino acid composition, the highest contents in muscle were observed in the normal salinity groups (25 and 30 ppt), while the amino acid content of hepatopancreas was significantly higher in the hypersaline-stressed groups (35 and 40 ppt) compared to the normal salinity groups (P < 0.05). The lipid content in the hepatopancreas was significantly higher than that in the muscle, and increasing profiles of PUFA were observed in both the muscle and hepatopancreas with increasing salinity. In conclusion, hypersaline stress (35 and 40 ppt) inhibited the growth and survival of juvenile ivory shells, and caused obvious gill damage, changes in the activities of stress-related enzymes and changes in the compositions of amino acids and fatty acids.