A BIOENERGETIC EXPLORATION OF PISCIVORY AND PLANKTIVORY DURING THE EARLY-LIFE HISTORY OF 2 SPECIES OF FRESH-WATER FISHES

In order to explore the trophic relationships of two different feeding strategies during the nursery period a bioenergetic model is applied to the early life history stages of a piscivore, the muskellunge (Esox masquinongy, Esocidae: Salmoniformes) and a planktivore, the bluegill (Lepomis macrochirus, Centrarchidae: Perciformes). The model uses a b alanced energy equation to predict consumption based on observed growt h and calculated losses to metabolism, excretion and egestion. Estimat es are temperature- and weight-dependent and are calculated on a daily basis over the duration of the nursery period. Ambient temperatures a nd the diet composition as determined from stomach content analysis we re used in the model. Comparisons of consumption and metabolic rates b etween a piscivore and a planktivore suggest that the planktivore has a much higher metabolic rate resulting in greater weight-specific cons umption and a larger maximum ration (g g(-1) day(-1)) than the piscivo re. The consumption of prey organisms in relation to prey standing cro p by the planktivore ranged up to 2.5% of the standing crop per day, w hereas in the piscivore population it approached 18% of standing crop per day; this suggests that consumption by the planktivore on the zoop lankton population in eutrophic Crane Lake would likely have less of a n effect on the prey population than that of the piscivore in bays of the St Lawrence River.