Production of monosex female groups of chinook salmon ( Oncorhynchus tshawytscha) by the fertilization of normal ova with sperm from sex-reversed females

Abstract

Three groups of chinook salmon were immersed for 2 h periods 4 and 11 days after hatching in water containing 17α-methyltestosterone at 400 μg/l. These groups were also administered the steroid in the diet at either 9 μg/g for 3 weeks, 3 μg/g for 6 weeks or 9 μg/g for 9 weeks. All but one of the adult fish examined were either mature or immature males. Maturation of the group fed 9 μg/g for 9 weeks was delayed relative to the other groups. Sperm collected from 14 chinook, which matured as 2-year-olds, was cryopreserved and used the following season with the sperm from 30 chinook which matured as 3-year-olds to fertilize separate groups of normal chinook ova. Sperm from an additional 15 3-year-old chinook was used to fertilize normal coho ova. Of the 44 chinook × chinook families seven were 100% female and another nine were > 92% female. Of the 15 chinook × coho families one was 100% female and another four were > 92% female. The results demonstrate the feasibility of producing monosex female groups of chinook salmon by the fertilization of normal ova with fresh or cryopreserved sperm from sex-reversed genetic females. These results provide the first experimental evidence for female homogamety in this species.