Comparisons of Salinity Tolerances and Osmotic Regulatory Capabilities in Populations of Sailfin Molly (Poecilia latipinna) from Brackish and Fresh Waters

Abstract

Sailfin mollies, Poecilia latipinna, inhabit both fresh and brackish waters throughout their native range. In laboratory analyses, following extensive acclimation, individuals taken from freshwater populations tolerated a range of ambient salinities from fresh water through 70%o (parts per thousand), whereas individuals from brackish water tolerated salinities ranging from fresh water through 80%0o. Plasma osmotic concentrations of the two groups were not significantly different at common ambient salinities over the range from fresh water through 75%0o. Isolation in nature of populations in fresh and brackish waters has not greatly altered their physiological capabilities with respect to ambient salinity.