Using aerobic exercise to evaluate sub-lethal tolerance of acute warming in fishes

We investigated whether fatigue from sustained aerobic swimming provides a sublethal endpoint to define tolerance of acute warming in fishes, as an alternative to loss of equilibrium (LOE) during a critical thermal maximum protocol (CTmax).  Two species were studied, Nile tilapia Oreochromis niloticus and pacu Piaractus mesopotamicus.  Each fish underwent an incremental swim test to determine gait transition speed (UGT), where it first engaged the unsteady anaerobic swimming mode that preceded fatigue.  After suitable recovery each fish was swum at 85% of their own UGT and warmed 1°C every 30 min, to identify the temperature at which they fatigued, denoted as CTswim.  Fish were also submitted to a standard CTmax, warming at the same rate as CTswim, under static conditions until LOE.  All individuals fatigued in CTswim, at a mean temperature approximately 2°C lower than their CTmax.  Therefore, if exposed to acute warming in the wild, the ability to perform aerobic metabolic work would b...