Effects of recombinant salmon type II growth hormone and bovine growth hormone on growth of coho salmon (Oncorhynchus kisutch)

A comparison of the efficacy of salmon and bovine growth hormone to stimulate growth of coho salmon juveniles was performed. Oncorhynchus nerka (sockeye salmon) type II growth hormone (nGH2) was produced using a bacterial expression system, yielding approximately 25 mg of refolded recombinant protein per litre of cells. The purified nGH2 and bovine growth hormone (bGH) were tested in juvenile O. kisutch (coho salmon) over 24 weeks. Weekly intraperitoneal injections of 0.1 and 0.5 mu g/g nGH2 resulted in a dose-dependent increase in weight and fork length compared to control fish injected with bovine serum albumin (BSA). Application of 0.5 mu g/g bGH resulted in the same stimulation of growth as did 0.5 mu g/g nGH2, indicating these proteins were equipotent. Following 6 weeks of treatment and a subsequent rest period of 7 weeks, coho salmon were further treated with bGH at 0.5 mu g/g. A prior treatment with bGH did not reduce growth-promoting activity of bGH in subsequent treatments. Throughout the experiment, condition factor decreased at similar rates for all treatment groups. These data show that bGH, which is widely available, can be used to elevate growth rate in juvenile salmon comparably to homologous GH, and validate the use of bGH in physiological or ecological experiments where rapid growth is desired compared to that seen in wild type.