Size-related metabolic responses of the pinfish, Lagodon rhomboides, to grouping, salinity variations, and sublethal petrochemical pollution

The single and combined effects of grouping, salinity variations, and sublethal petrochemical pollution on the respiratory metabolism of large and small pinfish, Lagodon rhomboides, were investigated. Fish in groups of four had a higher sustained swimming velocity but lower average metabolic rate than single fish. Increased swimming velocity, due to grouping, was greater with large pinfish. The metabolic rates of fish in groups of four were unaffected by sublethal pollution, while the metabolic rates of large single fish were elevated, and the rates of small single fish were depressed. Salinities of 20-45 ppt did not affect the metabolism of large or small pinfish in unpolluted water. The highest sustained swimming velocities were found at 20 ppt, for both large and small pinfish, and the velocities decreased as salinity increased. The sustained swimming velocities of large pinfish were decreased more than those of small pinfish. The sublethal pollution uniformly depressed small fish metabolism in all salinities. With large pinfish, pollution depressed metabolism in 20 and 32 ppt, but elevated metabolism at 45 ppt. Multiple regression analysis showed that salinity had a significant effect on metabolism only with large pinfish in polluted water with a 20-32 ppt salinity range