EFFECT OF FRESH-WATER ACCLIMATION ON THE SWIMMING PERFORMANCE AND PLASMA OSMOLARITY OF THE EURYHALINE GULF KILLIFISH

The objective of this research was to determine the effect of freshwat er acclimation on the swimming performance and plasma osmolarity of gu lf killifish Fundulus grandis. Fish were acclimated to either freshwat er or brackish water (10 parts per thousand salinity) for 10 d before experimentation. Plasma osmolarity was significantly lower in the fres hwater-acclimated fish; however, no significant changes occurred in pl asma osmolarity in fish recovering from a swim challenge at either sal inity. Critical swimming speeds of the fish acclimated to freshwater w ere significantly lower than those of fish acclimated to brackish wate r. Furthermore, the swimming challenge caused 40% mortality in the fre shwater fish but no mortality in the brackish-water fish. Acclimation of gulf killifish to freshwater environments appears to have a substan tial metabolic cost.