Influence of combinations of bovine growth hormone, 17α-methyltestosterone, and L-thyroxine on growth of yearling coho salmon (Oncorhynchus kisutch)

Abstract

Groups of yearling coho salmon held at 10 °C on a natural photoperiod, and fed excess ration daily, were administered either bovine growth hormone (bGH; 0.0092 IU/g body weight), L-thyroxine (T4; 1 μg/g), 17α-methyltestosterone (MT; 1 mg/kg diet), combinations of these hormones, or no hormone for 59 days. Fish received bGH and (or) T4 intramuscularly once weekly.Each individual hormone and hormone combination significantly enhanced growth. The sequence noted for growth rate of the groups was as follows: (bGH + MT + T4) > (bGH + MT) > (bGH + T4) > bGH > (T4 + MT) > MT > T4 > control groups. Three hormonal interactions were additive (T4 + MT; bGH + MT; bGH + MT + T4). The growth rate of fish treated with bGH + MT + T4 was over three times that of the controls.T4 or MT + T4 administration significantly increased condition factors, while MT, bGH, bGH + T4, bGH + MT, and bGH + MT + T4 decreased them.Significant elevations in percentages of muscle water (bGH) and lipid (T4; T4 + MT; bGH + MT) were found. Thyroid activity (follicle epithelial height) was significantly increased in MT and MT + bGH fish, but depressed in T4 fish. Hormone administration altered the histological structure of the endocrine pancreas (bGH and MT groups), ovary (bGH; MT groups), testis (MT groups), and interrenal tissue (bGH; MT).