Environment and Salinity Tolerance in the Genus Fundulus

Abstract

A comparison was made of environmental salinities, ability to survive in fresh water and upper salinity tolerance for over 20 species of the teleost genus Fundulus. All species of the genus occur, at times, in fresh water and are able to survive in this medium in the laboratory. Species found in brackish environments have upper salinity tolerances ranging from 74-114%o, while most species characteristic of fresh waters are unable to survive in salinities above 29%o. Notable exceptions are F. zebrinus, an inland species commonly found in saline waters, F. diaphanus, a freshwater form which often enters dilute brackish estuaries and F. waccamensis, a Pleistocene lacustrine derivative of F. diaphanus. Since brackish-water species are tolerant of life in fresh water while the reverse is not the case, it is suggested that freshwater species of Fundulus were derived from fully euryhaline ancestors which gradually lost the ability to live in sea water during extended isolation from brackish or marine environments.