INDUCTION OF STERILITY IN COHO SALMON (ONCORHYNCHUS-KISUTCH) BY ANDROGEN IMMERSION BEFORE 1ST FEEDING

Based on the observation that in coho salmon (Oncorhynchus kisutch) th e sensitivity to the effects of exogenous steroids is highest around h atching, and that it decreases as ontogenetic development progresses, immersion in a dilute solution of androgen prior to first feeding was examined as a means of inducting sterility in this species. Two approa ches were tested: 17alpha-methyltestosterone (MT) was administered eit her by continuous immersion for 30 days, from just before hatching to just before first feeding, at doses ranging from 3.12 to 100 mug/l, or as discrete 2-h immersions at doses of 1 or 10 mg/l, once or twice pe r week, for a total of 5 or 10 immersions, respectively. Sampling of f ish at about 7 months of age showed that these treatments had no signi ficant effect on survival or length, whereas weight was slightly reduc ed only in the groups exposed to the highest amount of androgen. At th e doses tested, discrete immersions resulted in a higher yield of ster ile fish (maximum 92.3%) than continuous immersions (maximum 51.2%). I n a subsequent experiment, 17alpha-methyldihydrotestosterone was compa red with MT in discrete immersions, but the percentage of sterile fish produced was not different from that obtained with MT. These results show that androgen immersion of coho salmon before first feeding can r esult in a high proportion of sterile fish without compromising their viability. The benefits for aquaculture derived from sterilizing salmo n before first feeding are discussed.