The early ontogeny of digestive and metabolic enzyme activities in two commercial strains of arctic charr (Salvelinus alpinus L.)

The extent to which growth performance is linked to digestive or energetic capacities in the early life stages of a salmonid species was investigated. We compared two strains of Arctic charr known to have different growth potentials during their early development (Fraser and Yukon gold). Trypsin, lipase, and amylase activities of whole alevins were measured at regular intervals from hatching through 65 days of development. To assess catabolic ability, we also measured five enzymes representing the following metabolic pathways: amino acid oxidation (amino aspartate transferase), fatty acid oxidation (beta-hydroxy acyl CoA-dehydrogenase), tricarboxylic acid cycle (citrate synthase), glycolysis (pyruvate kinase), and anaerobic glycolysis (lactate dehydrogenase). The measurement of these enzyme activities in individual fish allowed a clear evaluation of digestive capacity in relation to energetic demand. We also compared triploid and diploid individuals within the Yukon gold strain. For the whole experimental period, diploid Yukon gold fish exhibited the highest growth rate (1.08+/-0.18% length/day) followed by triploid Yukon gold fish (1.00+/-0.28% length/day) and finally Fraser strain fish (0.84+/-0.28% length/day). When differences in enzyme activities were observed, the Fraser strain showed higher enzyme activities at a given length than the Yukon gold strain (diploid and triploid). Higher growth performance appears to be linked to lower metabolic capacity. Our results suggest that fish may have to reach an important increase in the ratio of digestive to catabolic enzyme activities or a leveling off of metabolic enzyme activities before the onset of large increases in mass.