Effects of Salinity on Gills’ Chloride Cells, Stress Indices and Gene Expression of Asian Seabass (Lates Calcarifer, Bloch, 1790)

Abstract

Abstract A two-week research was carried-out to assess water salinity (WS) effects including 0, 15, 35 and 50‰ on osmoregulatory mechanisms and stress indices in Asian sea bass (34.4 g) juveniles. Except for fish reared at 50‰, in the other treatments gradually decreased to the prescribed WS during a 10-day period (-5‰ a day). After 10-day of acclimation period, fish reared at the prescribed WS for two weeks. Fish reared at 15 and 35‰ had higher chloride cell (CC) counts in the interlamellar region. The number of CC in the interlamellar region elevated with increment of WS up to 35‰, but they were pronouncedly reduced in 50‰ group . The diameter of CC in the interlamellar region was not affected by WS. The least nucleus diameter of CC in the interlamellar region was observed in fish reared at 15‰ (P < 0.05). The greatest and the least amounts of serum aspartate aminotransferase content were observed in fish reared at freshwater and 15‰, respectively. Fish reared at 35‰ had the highest serum sodium and potassium contents. Serum chloride content and total osmolality increased with increment of WS (P < 0.05). Serum cortisol and glucose contents gradually increased with elevation of WS up to 35‰, then their contents remarkably decreased. The relative expression of insulin like growth factor-1 in the liver of fish reared at 35‰ was strikingly higher than the other groups. The relative expression of HSP70 gene in fresh water group was pronouncedly elevated compared to other treatments. The relative expression of interleukin-1β in 15 and 35‰ groups was higher than the other groups; however, the relative expression of lysozyme gene in the liver of fish reared at fresh water was pronouncedly lower than the other treatments. The results of this study suggested rearing L. calcarifer at 15‰ closer to the isosmotic point and better provide its welfare.