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

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 (T 4 ; 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) T 4 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 + T 4 ) &gt; (bGH + MT) &gt; (bGH + T 4 ) &gt; bGH &gt; (T 4 + MT) &gt; MT &gt; T 4 &gt; control groups. Three hormonal interactions were additive (T 4 + MT; bGH + MT; bGH + MT + T 4 ). The growth rate of fish treated with bGH + MT + T 4 was over three times that of the controls.T 4 or MT + T 4 administration significantly increased condition factors, while MT, bGH, bGH + T 4 , bGH + MT, and bGH + MT + T 4 decreased them.Significant elevations in percentages of muscle water (bGH) and lipid (T 4 ; T 4 + MT; bGH + MT) were found. Thyroid activity (follicle epithelial height) was significantly increased in MT and MT + bGH fish, but depressed in T 4 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).