Swimming Performance of Coastal and Inland Largemouth Bass at Varying Salinities

Abstract

Coastal estuaries represent an interface between marine and fresh waters, and, as such, they are exposed to seasonal and annual fluctuations in salinity. All of the organisms that live in estuaries must emigrate or endure these variations. Largemouth Bass (Micropterus salmoides) is a freshwater fish that lives in coastal estuaries and has been shown to not migrate/move to avoid moderate seasonal increases in salinity. Additionally, these coastal Largemouth Bass have growth rates, condition factors, and life history strategies that differ from their inland counterparts. These differences suggest physiological adaptations to tolerate and even thrive in an estuarine environment. I compared swimming performance of Largemouth Bass from an Alabama estuary versus an inland reservoir at 0, 4, 8 and 12 ppt salinities to test for physiological performance-based adaptation to tolerate elevated salinities. I quantified critical swimming speed (CSS) of Largemouth Bass as a measure of swimming performance. I also took scanning electron microscopy (SEM) photos of gill filaments and lamellae of fish after swim tests to determine if there were any morphological differences among salinity treatments and between origin of the fish. CSS did not differ between inland and coastal Largemouth Bass nor were there significant effects of salinity. In addition, 12 inland Largemouth Bass were captured and tested during their spawning period and had significantly higher CSSs compared to non-spawning fish. SEM photos showed no evidence of adaptive gill remodeling or other morphological changes at any salinity or between inland and estuarine populations. It is still possible that inland and estuarine Largemouth Bass have different physiological mechanisms for tolerating salinity; however, if differences exist they were not measurable using swimming performance as a response metric.