Transfer of growth hormone (GH) transgenes into Arctic charr. (Salvelinus alpinus L.) II. Nutrient partitioning in rapidly growing fish.

To examine whether the utilization of protein and lipids is altered in the genetically modified, rapidly growing charr, we compared CMVOnGH1 transgenic and sibling fish. Muscle composition and rates of gas exchange were analyzed. Plasma metabolites were determined in the recently fed and post-absorptive state. No difference was found in muscle composition. At equal rates of protein accretion, the rate of NH4 excretion was 43% greater in sibling charr. The lower molar ratio of NH4 to O2 exchange implied the reduced expenditure of metabolized protein in transgenic charr. Plasma NH4 concentration in transgenic fish did not differ from that in sibling charr whereas the greater level of total CO2 indicated enhanced oxidation of non-protein nutrients. Decreased plasma triglycerides concentration and lower triglyceride to cholesterol ratio showed faster utilization of ingested lipids in transgenic charr, especially of energy-containing fraction. However, this was not accompanied with a reduced lipid content or altered fatty acid composition of muscle triglycerides or phospholipids. Comparative studies suggested that the transgenic charr had acquired features of domesticated salmonid fish. Their increased metabolic rate and enhanced utilization of dietary lipids, especially triglycerides, resembled the characteristics of domestic rainbow trout rather than wild counterparts.