Effect of different levels of salinity on gill and kidney function in common carp Cyprinus carpio (Pisces: Cyprinidae)

Abstract

Common carp is generally considered to be a stenohaline freshwater fish, but can tolerate a wide range of salinities and is therefore a good candidate for rearing in brackish water. The present study was undertaken to investigate the influence of environmental salinity on osmoregulatory mechanisms in the common carp (Cyprinus carpio). Seventy-five healthy adults of C. carpio were randomly divided into five groups kept in salinities of at least 3, 6, 9 and 12 g/l NaCl and a control (tap water) group. The salinity was gradually increased by 3 g/l daily, until the desired concentration for each group was reached. Then the urinary papilla was catheterized to allow urine collection. Urine was collected once daily for 14 days and after this period blood and gill tissue were sampled and plasma electrolytes and gill Na+–K+ ATPase activity were assayed. Plasma sodium and chloride significantly increased in response to increased environmental salinity (P≤0.05). Gill Na+–K+ ATPase activity had significantly increased in response to increased environmental salinity (P≤0.05). Our results showed that common carp can tolerate environmental salinities up to at least 12 g/l, but survival at salinities of at least 6 g/l and higher requires profound changes in function of gill and kidney as principal osmoregulatory organs.