Influence of environmental salinity and cortisol pretreatment on gill Na+/K+ −ATPase activity and survival and growth rates in Cyprinus carpio

Abstract The aim of this study was to investigate the effects of environmental salinity (2.5, 5, and 7.5‰), and cortisol pretreatment (0.01, 0.1, and 1 μg l −1 ) on gill Na + /K + -ATPase activity and survival and growth rates in a common carp, Cyprinus carpio (L.). Cortisol pretreated fish in water (0‰), showed a significant increase in gill Na + /K + -ATPase activity after 3 days of exposure when compared to that of the control groups. In contrast, cortisol pretreated fish exposed to various salinities (2.5, 5, and 7.5‰) showed a low level of gill Na + /K + -ATPase activity during the study period of 14 days. However, the gill Na + /K + -ATPase activity on day 7 th and 14 th day was found to be not significant (except 0.01 μg l −1 cortisol treatment at 5‰, and 7.5‰, respectively). We observed that the fish showed a great adaptation to all salinities and a higher survival rate during the study period. However, a long-term exposure study is needed to assess the effects of environmental salinity and cortisol pretreatments on these aspects for a desirable development in aquaculture practices.