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Salinity preferences of Fundulus heteroclitus and F. diaphanus (Pisces: Cyprinodontidae): their role in geographic distribution.

Salinity preferences and the effect of salinity acclimation on salinity preferences were determined for both the mummichog, Fundulus heteroclitus, and banded killifish, F. diaphanus. Experiments were conducted in a vertical salinity gradient consisting of layers at 0, 8, 14, 20, 26, and 31‰ salinity and at about 19C. Vertical-gradient tests were corroborated by retesting fishes in a two-compartment horizontal comparator. Mummichogs show a moderate preference for water of intermediate salinity (20‰) and a slight preference for 8‰. Banded killifish show a strong preference for fresh water. Neither species is affected by salinity acclimation. The differing preferences agree with their rarely overlapping natural habitat distributions.