Physiological responses to hyposaline exposure and handling and confinement stress in juvenile dolphin (mahimahi: Coryphaena hippurus)

Juvenile dolphin (mahimahi: Coryphaena hippurus) were exposed for 24 h to a reduced water salinity (20 ppt) to examine effects on selected aspects of metabolism, ionic regulation, hematology, and immune function. The oxygen consumption rate and gill Na+,K+-ATPase activity were significantly lower in water with 20-ppt salinity compared with full-strength seawater (34 ppt). These results may have reflected a decrease in osmoregulatory costs. There were no differences in any of the other variables associated with the salinity transfer. Plasma cortisol concentrations were significantly higher in the experimental tanks (200 L) than in the stock tank (2500 L), indicating a stress response elicited by handling and confinement in the smaller experimental tanks. In addition, handling and confinement significantly decreased plasma lysozyme activity and increased hematocrit levels, hemoglobin concentration, and erythrocyte and leucocyte numbers. There were no changes in liver glycogen content or plasma glucose, protein, or ion concentrations in response to salinity or handling or confinement during the experiment. This study is the first to provide information on selected physiological variables of juvenile dolphin and changes associated with an acute hyposaline exposure and handling or confinement stress.