Temperature preferences and tolerances of three fish species inhabiting hyperthermal ponds on mangrove islands

The temperature preferences and tolerances of Cyprinodon artifrons, Floridichthys carpio and Gambusia yucatana in shallow mangrove ponds off the coast of Belize were investigated. Parts of the ponds had a diurnal temperature change from 26C at night to 40C and above during midday. The hypothesis that behavioural partitioning of the ponds was occurring, cued by temperature, was tested. The 3 species were only usually seen in the ponds during midday. Pupfish (C. artifrons) preferred the warmer waters whereas the other 2 species stayed in the cooler areas. The critical thermal maximum (CTM) was determined for the 3 species. C. artifrons acclimated to a daily cycling temperature similar to the ponds had a CTM of 45.5C. Acclimation to a constant 30C lowered the CTM to 43.7C. F. carpio and G. yucatana acclimated to the cycled temperature had CTM of 43.9 and 43.3C, respectively and 42.5 and 42.6 for those acclimated to 30C. All 3 species could tolerate the high temperatures found in the ponds. There were large populations of C. artifrons in the ponds. This was probably because they used the whole pond during the day.