Temperature Tolerance of Nitrite-Exposed Channel Catfish

Upper temperature tolerances of channel catfish Ictalurus punctatus were determined with the critical thermal maximum (CTM) method after fish were exposed to various sublethal concentrations of nitrite for 24 hours at 20°C. The CTM was inversely related to nitrite concentration (r = -0.71; P < 0.01); group means ranged from 38.0°C for controls to 35.9°C for fish exposed to 1.4 mg NO2/L. As expected from previous studies, percent methemoglobin (a nonoxygen-carrying form of hemoglobin) was correlated with nitrite concentration (r = 0.85; P < 0.01), and thus was inversely correlated with CTM (r = -0.68; P < 0.01). These results indicate that nitrite-temperature interactions have the potential of adversely affecting the productivity of high-density channel catfish aquaculture systems, particularly those located in the southern U.S. during summer.