Development and evaluation of a western mosquitofish bioenergetics model

We developed a bioenergetics model for the western mosquitofish Gambusia affinis by combining data on temperature-dependent feeding rates with published information on respiration, temperature tolerance, and reproduction. To corroborate the model, we compared bioenergetics estimates with independent observations from laboratory feeding and growth trials. The model was then applied to a western mosquitofish population in Illinois to estimate feeding rates on natural prey taxa, including mosquito (Culicidae) larvae. Laboratory feeding experiments revealed that western mosquitofish have a high feeding capacity. Maximum consumption rates were 0.25-1.06 g(.)g(-1.)d(-1) at water temperatures between 5degreesC and 40degreesC; the highest feeding rates were observed at 32degreesC. Bioenergetics estimates of food consumption agreed well with laboratory measurements across a wide range of water temperatures (10-35degreesC). However, for fish experiencing negligible growth, model estimates of food consumption were higher than actual values measured in the laboratory. We postulate that at very low feeding and growth rates, activity costs may be overestimated by the model. Field-derived bioenergetics estimates of total food consumption ranged from 0.18 to 0.31 g of dry weight and were similar to those obtained from an empirical model relating western mosquitofish feeding and growth rates (0.15-0.39 g dry weight). Based on model simulations, we estimated that a typical age-0 western mosquitofish consumed about 1.990 mosquito larvae (2-68 larvae/d) from August 22 to October 8, 1998. Because the diets of free-ranging western mosquitofish were diverse, field-based estimates of mosquito consumption were generally lower than those reported for laboratory experiments, in which fish were fed only mosquito larvae. By accounting for diet composition in free-ranging western mosquitofish, the bioenergetics approach provides more realistic estimates of mosquito consumption than laboratory feeding experiments. Given recent concerns over the spread of West Nile virus, the model developed here should prove useful for quantifying western mosquitofish consumption in the context of both mosquito control and potential impacts on nontarget organisms.