A Test of 17α-Methyltestosterone as a Growth Promoter in a Coho Salmon Hatchery

Coho salmon (Oncorhynchus kisutch) fry reared at densities of 87–92 fish/m3 in hatchery ponds were fed a moist diet supplemented with 1 mg/kg 17α-methyltestosterone during a 7-month period. Hormone-treated fish grew faster and utilized food more efficiently than controls receiving the same diet without hormone. At the time of release from the hatchery, muscle of hormone-treated fish had slightly lower protein content than that of controls. Weight-to-length ratios and gonad development were not altered. Hormone treatment did not affect the rate of return of precocious males. Hormone-treated fish returned as 3-year-old adults to the hatchery almost as abundantly as control fish, but numbers caught in the fishery were reduced. Recent information indicates that the size of the released hormone-treated fish exceeded the most favorable size for maximum rate of return of adults. Both treated and control fish returned at higher rates than hatchery-production fish raised at higher densities. Egg viability and gonad structure of progeny of hormone-treated fish was normal, but male-to-female ratio was about 1, versus 1.25 for controls.