STUDIES ON GENOME MANIPULATION IN FISH I.INDUCTION OF TRIPLOID TRANSPARENT COLORED CRUCIAN CARP(CARASSIUS AURATUS TRANSPARENT COLORED VARIETY) BY HYDROSTATIC PRESSURE

This study was made to optimize hydrostatic pressure shock conditions for producing triploid transparent colored crucian carp (Carassius auratus transparent colored variety) by inducing second polar body retention. Shocks involving hydrostatic pressures of 600 kg/cm2 and 650 kg/cm2 for 3 minutes, applied 4 min or 5 min after fertilization, not only gave 100% triploidy as assessed by chromosome observation in the cells of embryos and fingerlings, but also produced relatively high rates of survival; the rates of hatching were about 90% relative to controls. Shocks applied at 6 min or later after fertilization had almost no effect on triploidization, and resulted in low survival rates. Shocks of hydrostatic pressures lower than 600 kg/cm2 (550 kg/cm2 or 500 kg/cm2) for 3 minutes resulted in a small proportion of diploids. Shocks of hydrostatic pressures higher than 650 kg/cm2 (700 kg/cm2 or 750 kg/cm2) for 3 minutes produced 100% triploidy but strongly affected the development of fertilized eggs, resulting in deformed embryos because of chromosome breakage and loss. The treatment of longer durations had the same effect as the treatment of higher pressures, which apparently disrupted the embryonic developmental processes. The longer the treatment duration, the higher the mortality. The results obtained from this study and those reported by other investigators seem to indicate that hydrostatic pressure shock may be an efficient method for performing chromosome set manipulation in fish, because the optimal conditions of hydrostatic pressure treatment are easy to obtain and the procedures of treatment are easy to standardize. The relationships between the optimal conditions and the percentage of triploidy as well as the survival rates were discussed. The causes for death under optimal and suboptimal conditions were analysed.