Effects of various salinities stress on the relationship between concentrations of ions, hormones in serum and gill mitochondrion-rich cells osmotic regulations of Epinephelus coioides junveniles

Effects of low salinity stress on the relationship between concentrations of ions, hormones in serum and gill mitochondrion-rich cells osmotic regulations of Epinephelus coioides juveniles were studied. E. coioides juveniles relayed in the seawater with salinity of 30 were directly transferred to water with salinities at 5, 10, 20, and 30, while those in seawater with salinity of 30 were taken as the control group. Na⁺, K⁺, Cl^– concentrations and cortisol (COR) in serum of E. coioides juveniles were investigated at 7 d and 15 d after transferring, and then the distributions and changes of the mitochondrion-rich cells (MRCs) in gills were studied. The results showed that Na⁺ and Cl^– concentrations in serum significantly increased with the rise of water salinity (P<0.05), while there were no significant differences with K⁺ concentration at different salinities (P>0.05). COR level in water with salinities 5 and 10 were significantly higher than that in water with salinity 20 and the control group (P<0.05). The volume and quantity of MRCs were increased, and the volume of MRCs in water with salinity 20 and control group were significantly greater than that in water with salinities 5 and 10 (P<0.05). There was a special apical membrane in gill MRCs. The apical surfaces of gill MRCs in water with salinities 5 and 10 were generally flat with dense microvilli-like projections. In contrast, the gill MRCs in water with salinity 20 control group exhibited deeply invaginated surfaces with smaller orifices without projections In the light of this study,E. coioides juveniles can survive in water at salinities above 5, and the fresh water aquiculture of E. coioides is feasible.