Evaluation of Cross-Protection in Channel Catfish

Heat treatment initiates cellular responses that are often attributed to an increased resistance to subsequent acute stressors; a phenomena referred to as cross-protection (CP). For example, when heat treatments were applied to groups of channel catfish fingerlings, an increase in upper critical temperatures was observed 24, 48, and 96 h later. We have also observed CP in channel catfish exposed to other water quality extremes.  In a series of experiments we assessed CP by measuring the time at which heat hardened and control channel catfish lost equilibrium (LE) when they were exposed to extreme water quality conditions.  Heat hardened channel catfish maintained equilibrium for longer time periods in 35 ppt NaCl than controls at 48 and 96 h after heat treatment.  CP to extreme pH was also observed; 96 h after heat treatment the mean time to LE in pH 10.9 was significantly greater for heat hardened channel catfish than for controls.  These results provide a template for further study of CP in channel catfish. We are currently evaluating CP induction methods, the time course and cellular mechanisms for this response in order to determine if the machinery involved with CP can be used to mitigate fish stress.