LIPID DYNAMICS AND GROWTH RELATIVE TO RESOURCE LEVEL IN JUVENILE EASTERN MOSQUITOFISH (GAMBUSIA-HOLBROOKI, POECILIIDAE)

We examined early energy allocation patterns of eastern mosquitofish (Gambusia holbrooki) reared on three dietary regimes by measuring growth and lipid storage at several points during the first 40 days of life. A high food treatment produced growth increments similar to those previously found in natural mosquitofish populations, whereas intermediate (one-half the quantity of high) and low (one-quarter the quantity of high) food treatments produced significantly lower growth increments. Lipid content was about 20% of dry mass at birth and declined for the first five days of life in all three treatments. After this initial period of lipid use, lipid levels increased asymptotically in all treatments. Lipid content was positively correlated with feeding level and plateaued at significantly different levels for each treatment. These three laboratory-reared groups had significantly higher percent somatic lipids than two populations of wild fish of similar size, probably because of differences in food and activity levels between laboratory and field environments, Size at birth was positively correlated with size at two weeks of age but was not significantly correlated with size beyond 15 days of age. Birth size was uncorrelated with subsequent growth or lipid content. No trade-offs between growth and lipid storage were found at any level examined in this study. We suggest that differences in energy acquisition or metabolic efficiency may swamp differences in resource allocation between these two energy compartments.