Effects of salinity on O₂ consumption, ROS generation and oxidative stress status of gill mitochondria of the mud crab Scylla serrata.

Mitochondrial respiration, activities of electron transport chain enzymes and formation of oxidative stress parameters were investigated in mitochondria isolated from gill tissue of mud crabs (Scylla serrata) as a function of salinity (10 ppt, 17 ppt and 35 ppt). Mitochondrial oxygen consumption rate was higher for succinate as substrate compared with those of glutamate, malate and pyruvate. Complex I and complex II mediated respirations were higher at low salinity (10 ppt) than high salinity (17 ppt and 35 ppt). Although activities of electron transport chain enzymes particularly complexes I (EC 1.6.5.3), II (EC 1.3.99.1) and II-III (EC 1.3.2.1) were elevated linearly in response to salinity treatment, activity of complex V (ATPase, EC 3.6.1.34) was decreased at 35 ppt salinity. However, ATPase activity was higher at 17 ppt salinity in comparison to 10 ppt and 17 ppt salinity. Results of the experiment suggest that high salinity (35 ppt) causes hypoxic state in mitochondria of mud crabs. Hypoxic condition induced by high salinity was accompanied with increased hydrogen peroxide production resulting oxidative stress in mitochondria of crabs. A possible mechanism of hypoxia-induced reactive oxygen species generation and OS due to salinity stress in the crabs is discussed.