EFFECTS OF ENVIRONMENTAL TEMPERATURE ON THE METABOLIC AND ACID-BASE RESPONSES OF RAINBOW TROUT TO EXHAUSTIVE EXERCISE.

In vivo experiments were conducted to determine how the physiological response to exhaustive exercise in rainbow trout (Oncorhynchus mykiss) is affected by environmental temperature. The white muscle acid­base status (e.g. pH, PCO2, HCO3- and deltaH+m) and metabolite (e.g. lactate, phosphocreatine, ATP and glycogen) content, and the acid­base status and lactate concentrations in the blood, were measured at rest and during recovery from burst exercise in rainbow trout acclimated to either 5 or 18 °C. Trout acclimated to the warmer temperature had higher resting levels of white muscle phosphocreatine (PCr) and also utilized a greater proportion of their muscle ATP and glycogen stores during burst activity compared with trout acclimated to the colder temperature. Recovery of muscle PCr and glycogen levels was independent of acclimation temperature, but muscle ATP levels recovered faster at 18 °C. Exhaustive exercise resulted in a similar lactacidosis in the muscle of trout acclimated to either temperature. In contrast, temperature had a marked influence on the lactacidosis in the blood. Blood lactate and metabolic proton concentrations following exercise were about twofold greater in fish acclimated to 18 °C than in fish acclimated to 5 °C. Despite the more severe acidosis and the greater lactate accumulation in the plasma of fish acclimated to warmer temperatures, the time required for recovery of these variables was similar to that at 5 °C. Taken together, these results suggest that acclimation temperature does not significantly affect anaerobic capacity in rainbow trout, but may account for much of the documented variability in the dynamics of the lactacidosis in blood following exhaustive exercise in fish.