Ontogenetic and Seasonal Patterns in the Energy Content of Piscivorous Fishes in Lake Superior

Abstract

Ontogenetic, seasonal, and sex-related patterns in energy density (J/g wet mass) was studied in burbot ( Lota lota), lean lake trout ( Salvelinus namaycush namaycush) and siscowet lake trout ( Salvelinus namaycush siscowet) collected from Lake Superior in 1996 and 1997. Energy density was strongly negatively correlated with water content for all fishes (r 2 = 0.86 to 0.99). For fishes of comparable size, energy density of siscowet (10.8 kJ/g) was significantly higher than lean lake trout (7.8 kJ/g) and both were significantly higher than burbot (5.1 kJ/g). Energy density in spring was higher in lean and siscowet lake trout, and lower in burbot than in other seasons. No significant differences were apparent between sexes within a species. Energy density increased in a predictable fashion with body mass for lean and siscowet lake trout, but varied without trend for burbot. The regression common to the three species (kJ/g wet mass = 36.78 – 0.41(% water), p < 0.001) provides a straightforward method for estimating ontogenetic and seasonal energy density in these fishes.