Growth increments and some flesh and gonad characteristics of juvenile coho salmon receiving diets supplemented with 17α-methyltestosterone

Juvenile coho salmon Oncorhynchus kisutch (Walbaum) received a diet of Oregon Moist Pellets supplemented with either 10, 1, 0.2 or 0 ppm of 17α-methyltestosterone for 72 weeks. The fish were held in fresh water during the first 57 weeks and in salt water during the remaining time of the study. At the end of the fresh water residency, the fish receiving 10 and 1 ppm of steroid showed a net increase in weight of 125 and 71 % respectively over the controls. Both test groups also gained in length, but the 10 ppm group gained proportionately less, which resulted in a thicker body. After transfer to salt water at the normal time of smolting, there was a decrease in the rate of growth in weight and length of the two groups receiving the high doses of steroid. The decrease was most noticeable in the 10 ppm group and a number of mortalities occurred in this group. Testes of fish receiving 10 ppm of the steroid became hypertrophied and later degenerated with loss of spertnatogonia; the ovaries were not affected. 17α-methyltestosterone fed at 10 ppm for 49 weeks increased the lipid content of the flesh from 2.4 to 3.5 % and decreased the amount of flesh from 35.0 to 28.5 % of body weight. No change in the moisture content was found. External changes noted in the 10 ppm group included loss of silvering, deepening of the body, particularly in the region of the anal fin, and widening of the lower jaw.