PRODUCTION OF FEMALE TRIPLOID COHO SALMON (ONCORHYNCHUS-KISUTCH) BY PRESSURE SHOCK AND DIRECT ESTROGEN-TREATMENT

The aquaculture production of all-female triploid (sterile) population s is recognized as being of potential advantage for many species of fi sh where sexual maturation is not desired. All-female triploids have b een produced by inducing triploidy in eggs that had been fertilized wi th monosex female sperm. However, monosex stocks to produce this type of sperm are currently available only for a limited number of economic ally important species. To circumvent this problem, an alternative met hod would be the direct feminization of tripoid embryos. In Pacific sa lmon, pressure shocks applied shortly after fertilization have consist ently resulted in high yields of tripoids, and feminization by direct estrogen treatment has also been shown to be highly effective if appli ed shortly after hatching. In this study, coho salmon eggs were made t riploid by a pressure shock of 633 kg/cm2 for 4 min, applied 20 min af ter fertilization and incubation at 10-degrees-C. Some of the resultin g embryos were then feminized with estradiol-17beta in single 2-hour i mmersion treatments at 400 mug/liter, administered 1 and 8 days after hatching. Six months later, when the fish were juveniles, analysis of the DNA content of erythrocytes by flow cytometry revealed a 100% indu ction of triploidy, while histological examination of the gonads showe d 82 % females, which were completely devoid of oocyte development and thus genetically sterile. These manipulations reduced survival during early stages of development but survival became stable later. Togethe r, these results suggest that the production of sterile fish by direct feminization of induced triploids could be of particular advantage fo r those species in which all-female stocks are yet not available or di fficult to obtain.