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).