TEMPERATURE CONSTRAINTS ON OVERWINTER SURVIVAL OF AGE-0 WHITE PERCH

We evaluated the relative importance of energy depletion and osmoregul atory stress as possible mechanisms regulating overwinter mortality of age-0 white perch Morone americana. Fish used less energy, took up mo re water, and had much higher mortality at 2.5 degrees C than at 4.0 d egrees C. Mortality, energy use, and water uptake were all related to body size. Relationships of empirically derived endurance time (ET, da ys to 50% mortality) to body mass were allometric with weight exponent s of 0.29 at 2.5 degrees C and 0.77 at 4.0 degrees C. Theoretically de rived weight exponents were 0.82 for ET models based on starvation and 0.18 for models based on osmotic mechanisms. The theoretical and empi rical models suggest that overwinter mortality of white perch is cause d primarily by starvation at 4.0 degrees C and by osmoregulatory dysfu nction as well as starvation at 2.5 degrees C.