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 transgeni c and sibling fish. Muscle composition and rates of gas exchange were analy zed. Plasma metabolites were determined in the recently fed and post-absorp tive state. No difference was found in muscle composition. At equal rates o f protein accretion, the rate of NH4 excretion was 43% greater in sibling c harr. The lower molar ratio of NH4 to O-2 exchange implied the reduced expe nditure of metabolized protein in transgenic charr. Plasma NH4 concentratio n in transgenic fish did not differ from that in sibling charr whereas the greater level of total CO2 indicated enhanced oxidation of non-protein nutr ients. Decreased plasma triglycerides concentration and lower triglyceride to cholesterol ratio showed faster utilization of ingested lipids in transg enic chair, 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 th at 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 rainb ow trout rather than wild counterparts. (C) 1999 Elsevier Science B.V. All rights reserved.