TEMPERATURE TOLERANCE OF THE SHEEPSHEAD MINNOW, CYPRINODON-VARIEGATUS

The sheepshead minnow may be the most eurythermic of all known fishes. This species' physiological (static or plunge) and ecological (dynami c) thermal tolerance polygons have areas of 1380 C-2 and 1470 C-2, res pectively, which are among the largest ever measured for a fish. Zn ad dition, sheepshead minnows are more resistant to both high and low let hal temperatures than are other fish species. Sheepshead minnows accli mated to 5 and 30 C have CTMin-CTMax of 0.6-34.6 C and 11.3-44.2 C, re spectively. The CTMax increased to 45.1 C for fish exposed to a thermo period of 37-42 C for 30 days. At temperatures below 10 C, fish burrow into the substrate, presumably to maintain body temperatures above th e lower physiological limit of -1.8 C. Physiological and behavioral ad aptations allow sheepshead minnows to survive in extreme tidal pool ha bitats where temperatures can range from -1.9-43 C.