Annual cycle of energy allocation to growth and reproduction of yellow perch

Growth (length, weight) of yellow perch Perca flavescens in western and wes t-central Lake Erie began between June and July. possibly reaching asymptot ic size by early winter. Energy density (kJ g(-1)) of somatic tissue increa sed markedly from June to September, then declined to low levels by the fol lowing spring. Consequently, energy mass (kJ) of somatic tissue increased t o September and then declined slowly until March. Ovarian growth began in O ctober, and the size of the ovaries was maximal in April, just before spawn ing in May. The energy density of ovaries, however, increased to a peak in December, and then declined. The increase in ovary size in the winter, ther efore, resulted largely from an allocation of tissue of low energy density. Fecundity and gonad size were correlated with somatic and gonadal energy d ensity. A bioenergetics model was used to describe the monthly allocations of energy to respiration, growth, excretion, and reproduction. Most direct reproductive costs (80%) were incurred from September to December, correspo nding to the cycle in the activity of the liver. Energy acquired in the ear ly summer may be critical for determining maturation, fecundity, and egg qu ality. From 1978 to 1990, <80% of the females from the western and west-cen tral basins of Lake Erie were classed as spent in July.