Critical Thermal Maxima Of Two Geographic Strains Of Channel and Hybrid Catfish

Critical thermal maxima have long been used to provide a relevant and ecologically valuable thermal reference point, identifying the first signs of stress. In catfish pond culture, daily temperature maximums up to 36°C and fluctuations up to 6°C are currently observed. These extreme conditions are likely to be exacerbated by the effects of global climate change. Channel catfish (Ictalurus punctatus) have a broad natural distribution from southern Canada to northern Mexico. It was hypothesized that regional genetic differences would cause strains with an originally southern natural range to have greater thermal tolerance relative to strains with a natural northern range, and consequently a greater critical thermal maxima. Hybrid catfish (I. punctatus x [blue catfish] I. furcatus) strains were expected to have a greater critical thermal maxima than their respective channel catfish strains due to a more southern distribution of blue catfish. To examine this, we quantified short term acute thermal tolerance differences of two geographically distinct strains of channel catfish and the corresponding industry standard blue catfish hybrid cross. Catfish were subjected to water temperature increase at a rate of 2.0±0.1°C hour^-1 until loss of equilibrium occurred. Southern channel catfish were able to tolerate higher temperatures than northern. Channel catfish tolerated higher temperatures than hybrid strains. This study indicates that geographically distinct catfish strains differ in acute thermal tolerance, suggesting genetic control.