Effects of simulated cold fronts on the survival and behaviour of yellow perchPerca flavescensyolk-sac fry

Abstract

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°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°C. Fry remained at the bottom of the tanks for the entire 48 h simulated cold-front. Fry resumed swimming activity once water temperatures began to increase (by approximately 6°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.