Rates of Gain and Loss of Heat Tolerance in Channel Catfish

Abstract

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 differences between initial and final acclimation temperatures, as well as by the direction of temperature change, but were inversely related to the magnitude of the final acclimation temperature. Interrelationships among these variables were accurately described by highly significant multiple-regression models (P < 0.0001; R ² > 0.98). These models predict that fish transferred from 10°C to 20°C, from 20°C to 30°C, or from 30°C to 35°C were reacclimated within 21, 12 and 3 d, respectively. Reciprocal transfers resulted in respective reacclimation times of 54, 30 and 9 d. These times were twice those previously measured for resistance acclimation of channel catfish.