Metabolic Effects of Bovine Growth Hormone and Genetically Engineered Rainbow Trout Growth Hormone in Rainbow Trout (Oncorhynchus mykiss) Reared at a High Temperature

The growth promoting ability of bovine growth hormone purified from natural sources (bGH) and genetically engineered rainbow trout growth hormone (rtGH) were compared in rainbow trout (Oncorhynchus mykiss) reared at 17.0 °C. Fish were fed high (on-demand feeding) and low (2.8–4.6% of body weight/d) rations. On both rations, length specific growth rates were significantly higher in bGH treated fish than in all other treatments. No significant differences in weight specific growth rates were detected between treatments. Testosterone levels in fish fed the high ration and treated with 1.0 μg/g rtGH or bGH were significantly elevated compared with controls as were 17-β-estradiol levels in females. bGH significantly reduced condition factors of low ration fish, and bGH and rtGH significantly depressed hepatosomatic indicies of high ration fish compared with controls. In a second experiment, weight and length specific growth rates were higher in rtGH and bGH injected fish than in saline controls but these differences were not significant. DNA standardized RNA levels were higher in rtGH and bGH treated fish than in saline control fish and these differences were significant in bGH treated fish. Results indicate that at high rearing temperatures GH administration does not have a major influence on growth but does stimulate steroidogenic and metabolic activity.