Production of All-Female and Sterile Coho Salmon, and Experimental Evidence for Male Heterogamety

In May 1977, groups of coho salmon Oncorhynchus kisutch were immersed in 17β-estradiol or 17α-methyltestosterone in the eyed-egg and alevin stages. Treatments were continued during the early fry stage via administration of a diet containing the steroids. The estradiol groups and the control were spawned in December 1979. The estradiol groups contained 96–100% females compared with 54% female fish in the control. The methyltestosterone groups were comprised primarily of sterile fish. The ova from 23 females in each of the estradiol groups and 22 control females were fertilized with normal milt and offspring were reared to 9 months of age, at which time male: Female ratios were determined. There was no significant difference in survival between treated and control families. Half of the families from estradiol-treated fish had a 3:1 male: Female ratio, indicating male heterogamety. The two methyltestosterone-treated groups continued to grow during the 1-year period following the spawning of the control group.