Conditions to Induce Triploid and Gynogenetic Diploid in Ayu Plecoglossus altivelis

The ploidy manipulation was applied in breeding ayu Plecoglossus altivelis to examine the condition needed to induce triploids and gynogenetic diploids at successful rates with high survival rates. First, ultraviolet (UV) ray doses between 0–19260 erg/mm² were tested to inactivate sperm genetically. Then, cold shock treatment at 0-0.5°C for 30 or 60 min were conducted to detain the 2nd polar body in fertilized egg. The best elapsed time before the start of the cold shock was examined between 0–15 min. Based on the appearance of the haploid syndromes in the embryo, a dose of UV ray of at least 6000 erg/mm² was required to inactivate sperm genetically. An elapsed time of 4 to 6 min was required before the start of cold shock after insemination. Gynogenetic diploid embryos before hatching had a survival rate of 54% at optimum induction whereas triploid embryos survived 61 % under the same conditions using same egg lot. The success rate of inducing triploid based on chromosome counts, was 100% using normal sperm and eggs cold shocked at 6 min after insemination for 30 or 60 min. The success rate of inducing gynogenetic diploid based on chromosome counts was also estimated to be 100% using UV (9630 erg/mm²) irradiated sperm after which the ferilized eggs were cold shocked.