COMPARISON OF HYDROSTATIC-PRESSURE AND THERMAL SHOCKS TO INDUCE TRIPLOIDY IN COHO SALMON (ONCORHYNCHUS-KISUTCH)

Hydrostatic pressure or thermal shocks were administered to coho salmo n eggs 20, 40, 60 and 80 min post-insemination. Pressure shocks ranged from 6.2 to 8.4 x 10(4) kPa, and lasted 4 min. Thermal shocks ranged from 24 to 28-degrees-C, and were applied for durations of 10 and 20 m in. Triploid induction rate for each treatment group was evaluated by measurement of erythrocyte DNA content using flow cytometric analysis. Triploid rates Of 100% were produced by pressure shocks of 6.9-8.3 X 10(4) kPa for eggs 20 min post-fertilization and by thermal trauma of 28-degrees-C for 20 min, 20 min after fertilization. Survival was inve rsely correlated with the intensity of treatments. Thus, triploid yiel ds calculated as the product of the triploid rate and the numbers surv iving to hatch, expressed as a percentage of the number of eggs origin ally present in the groups, were highest with a hydrostatic pressure t reatment of 6.2 X 10(4) kPa for 4 min treatment, 20 and 40 min after f ertilization or a beat shock of 26-degrees-C for 20 min treatment, 20 min after fertilization.