Physiological indicators of salinity stress in the grey mullet, Mugil cephalus, Linnaeus, 1758 juveniles

Grey mullet ( Mugil cephalus ) juveniles were subjected to salinity stress in order to determine physiological response and recovery. Variations in the most important blood physiological indicators of stress (i.e., cortisol and glucose) were analyzed after application of stress. According to the results, the concentration of cortisol increased significantly 30 min after delivery of fish to water with 15 and 25 ppt salinities. The elevated levels of cortisol returned to basal levels 60 min after application of stress ( P > 0.05). Plasma cortisol and glucose did not show significant changes after delivery of fish to water with 35 ppt salinity ( P > 0.05). The elevation of plasma glucose occurred 30 and 60 min after delivery of fish to water with 15 and 25 ppt salinities ( P > 0.05). Our study demonstrated that low salinities are stressful for grey mullet juveniles.