Physiological Responses of Largemouth Bass, Micropterus salmoides, Exposed to Salinity

Abstract

Plasma osmotic and electrolyte concentrations as well as branchial Na⁺/K⁺ and Mg⁺⁺ ATPase activities were determined in the field for largemouth bass, Micropterus salmoides, from a brackish marsh and freshwater lake in southcentral Louisiana. Laboratory experiments were conducted to evaluate plasma chemistry and gill ATPase activities of largemouth bass from both locations exposed to 0, 4, 8, and 12‰ salinity. No significant differences in physiological responses were detected between marsh and freshwater largemouth bass exposed to 0, 4, or 12‰. Exposure to 12‰ salinity resulted in osmotic stress in largemouth bass from both locations. At 8‰, marsh largemouth bass had significantly higher plasma solutes and lower gill ATPase activities than freshwater fish. Different physiological responses by marsh and freshwater largemouth bass during exposure to 8‰ salinity indicated that marsh largemouth bass have adapted to environments of variable salinity by reducing active ion transport and tolerating elevated plasma son levels.