The effects of temperature on the development and mortality of eggs of perch, Perca fluviatilis

SUMMARY. The rate of development and mortality of perch Perca fluviatilis was studied at ten different constant temperatures. The rate of development was inversely related to the incubation temperature, whereas the rate of mortality was directly related to the incubation temperature. The sum of heat (ΣH, degree‐days) required for 10, 50 and 90% of the eggs to hatch was found to be constant, regardless of the incubation temperature, with mean values (with 95% confidence limits) of 91.4 (83.3–102.0) degree‐days above 4.6°C for 10% hatched, 97.0 (90.9–104.2) degree‐days above 4.9°C for 50% hatched and 101.0 (94.3–108.7) degree‐days above 5.0°C for 90% hatched. Mortality among the different embryological stages was highest for the pre‐hatching stage (i.e. when eye‐pigment has been formed) at all temperatures. High mortality among the early stages occurred at temperatures below 8°C and above 12°C.