Upper range thermal stress tolerance in channel and hybrid catfish strains

Channel catfish (Ictalurus punctatus) have a broad distribution from Canada to Mexico, suggesting that different strains may have different thermal tolerances. In aquaculture, daily temperature maximums up to 36-40°C and fluctuations of 3-6°C occur, and may be exacerbated by future climate change. To quantify differences in thermal tolerance amongst geographically-distinct channel catfish strains and corresponding hybrid catfish (I. punctatus x [blue catfish] I. furcatus): acute critical thermal maximum (CTmax), and the effects of chronic thermal regimes on growth, survival and differential gene expression were examined. Southern channel catfish had higher CTmax than northern, and channel catfish had higher CTmax than hybrid catfish. Under chronic thermal stress, hybrid catfish had the greatest survival and most consistent growth. Further, northern channel catfish had the greatest magnitude and largest amount of upregulated gene transcripts in response to high temperatures, indicating greater thermal stress. Therefore, catfish thermal tolerance varies by geographic region and species.