Swimming Performance of Coastal and Inland Largemouth Bass at Varying Salinities

Coastal estuaries are an interface between marine and fresh waters, and therefore, experience seasonal and annual fluctuations in salinity.  Estuarine organisms must adapt, emigrate, or endure these potentially stressful variations. Largemouth bass (Micropterus salmoides)  that live in oligohaline estuaries have been shown to not migrate to avoid increases in salinity. Additionally, coastal largemouth bass have growth rates, condition factors, and life history strategies different from their inland counterparts. These differences suggest physiological adaptations to tolerate and thrive in an estuarine environment. We compared Critical Swimming Speed (CSS), a measure of swimming performance, of largemouth bass (279-432 mm) from an Alabama estuary versus an inland reservoir at 0,4,8 and 12 ppt salinities to test for performance-based adaptation to tolerate elevated salinities. CSS of inland bass was significantly less than for coastal bass, and all fish had significantly slower CSS at 12 ppt versus other salinities. Coastal bass had significantly higher liver weight relative to total weight than inland bass perhaps related to physiological adaptation. Given these differences, management decisions, including potential stocking, should include consideration of such local adaptations.