Estimating the Energy Density of Fish: The Importance of Ontogeny

Abstract

Ontogenetic patterns in the percent dry weight (%DW) and energy density (joules per gram of wet weight) were studied in the early life stages of the subtropical estuarine and marine gray snapper Lutjanus griseus and the warm-temperate estuarine and marine spotted seatrout Cynoscion nebulosus. The %DW was variable for individuals of both species but increased significantly through larval to juvenile stages (<20% for fish <50 mm standard length to 20–30% for fish >50 mm). The lipid percentage, which was determined only for gray snapper, was also variable between individuals but showed significant increase with body size. Strong relationships between percent dry weight and energy density were evident for both species; however, the slopes of regressions were significantly lower than in general multispecies models, demonstrating the need for species- and stage-specific energy density data in bioenergetics models.