Seasonal Changes of Fat Content in the Yellow Perch (Perca flavescens) of Two Laurentian Lakes

Different body fat reserves in male and female yellow perch (Perca flavescens) may determine a marked differential mortality during the winter. This was revealed by a study in two Laurentian lakes of the Province of Quebec harboring stunted yellow perch with a marked predominance of males. The proportion of females in each year-class is markedly smaller, thus suggesting a higher mortality among immature and mature females than among males.In an attempt to explain the differential mortality, the seasonal variation of body fat content in males and females was measured; also the fat level at time of death caused by starvation under laboratory conditions was determined. The results showed that in the females the body fat content falls to a critical level of about 2% at least 4 mo before spawning, whereas the males maintain a fat level of almost 5% throughout winter.