Euryhaline adaptations in the fat sleeper, Dormitator maculatus

Salinity tolerances and plasma osmotic concentrations were determined in the fat sleeper, Dormitator maculatus, a common species in estuarine and coastal fresh waters along the Atlantic and Caribbean coasts of North, Central and South America. Analyses followed sequential laboratory acclimations to a series of ambient salinities at a constant temperature of 20 ± 1° C and photoperiod of 12L: 12D. These fish tolerated a range of ambient salinities from fresh water through a salinity of 75‰. Plasma osmotic concentrations were regulated at an essentially constant level in the salinity range from fresh water through a salinity of 50‰, beyond which plasma concentrations trended upward with increased ambient salinity. We conclude that D. maculatus, while truly euryhaline, docs not show the extreme euryhalme capabilities of several teleost fishes that are ‘full‐time’ estuarine inhabitants.