Effects of simulated cold fronts on the survival and behaviour of yellow perch Perca flavescens yolk-sac fry

Acute reductions in water temperature (i.e. cold fronts) may influence larval fish survival directly via limits on physiological tolerance or indirectly by acting as a sublethal stressor. The primary objective was to quantify survivorship of yellow perch yolk-sac fry exposed to two different temperature declines (4 and 8 degrees C) and compare survivorship to that of perch fry under ambient temperatures representative of natural conditions. Behaviour of yolk-sac fry following temperature declines was also qualitatively assessed. Mean survival in the control, 4, and 8 treatment tanks was 90, 91 and 97%, respectively, and no significant differences in percent survival were observed between the control and the 4 treatment (ts=0.10; df=7; P=0.93), the control and 8 treatment (ts=1.85; df=7; P=0.11) or the 4 and 8 treatments (ts=1.33; df=7; P=0.22). Observations of yellow perch eggs and fry behaviour following temperature declines differed among treatments. Any remaining eggs in the control treatment and 4 treatments continued to hatch during the experiment, and fry were documented swimming throughout the water column in all tanks. However, in the 8 treatment, any eggs that had not hatched remained inactive and all fry within all 8 treatment tanks ceased swimming activity and settled to the bottom of the tanks once the temperature reached 3.9 degrees C. Fry remained at the bottom of the tanks for the entire 48h simulated cold-front. Fry resumed swimming activity once water temperatures began to increase (by approximately 6 degrees C). Results indicated that drops in temperature (i.e. cold fronts) similar to or greater than those found in small impoundments did not cause direct mortality of yellow perch during the yolk-sac fry (post-hatch larvae) stage. Although an acute drop in temperature may not induce sudden high mortality, it may be a sub-lethal stressor, leading to increased starvation or predation risk.