Rates of Gain and Loss of Heat Tolerance in Channel Catfish

Thermal acclimation dynamics of channel catfish Ictalurus punctatus were quantified by using time-series critical thermal maximum (CTMax) estimates. Data consisted of CTMax determinations from 57 groups of 10 fish each. Respective CTMax values ranged from 30.9°C to 42.1°C for acclimation temperatures between 10°C and 35°C and increased 0.45°C for each 1°C increase in acclimation temperature. Rates of heat tolerance gain for fish transferred from low to high temperatures were not constant but decreased geometrically with respect to time until end-acclimation levels were reached. Fish transferred from high to low temperatures showed similar geometric patterns of tolerance loss; however, progressive decrease in CTMax was relatively slow and was interrupted after 24 h by a consistent 72-h acclimatory stasis. Differential patterns of heat tolerance gain and loss suggest that both processes place a premium on heat tolerance conservation. Acclimation times were influenced directly by absolute difference...