Wayne A. Bennett, Susan J. Allee, Thomas L. Beitinger, and Robert W. McCauley. University of West Florida, Department of Biology, 11000 University Parkway, Pensacola, FL 32514

Abstract. Thermal acclimation dynamics of channel catfish, Ictalurus punctatus, were quantified using time-series critical thermal maxima (CTMaxima) determination. Data consisted of CTMaxima determined for 57 groups of 10 fish each. Respective CTMax values ranged from 30.9 to 42.1^oC for acclimation temperatures between 10 and 35^oC and increased 0.45^oC per 1^oC increase in acclimation temperature. Heat tolerance accruement progress in a smooth, decreasing geometric pattern, whereas attrition was interrupted after 24 h by a consistent 72 h acclimation stasis. Acclimation times were influenced directly by the magnitude of the temperature change and inversely by final acclimation. Interrelationships among these parameters are accurately described by highly significant multiple regression models (P < 0.0001; R² > 0.98). The models predict that fish transferred from 10 to 20, 20 to 30, or 30 to 35^oC are reacclimated within 21, 12, and 3 d, respectively. Reciprocal transfers resulted in respective reclamation times of 54, 30 and 9 d. These times are twice those previously measured for this species using resistance time studies; however, the differences are probably related to the disparate methodologies. Although acclimation was fastest at higher temperatures, acclimation times were driven by smaller differences between initial and final CTMaxima and not increased acclimation rates.