Triploid induction of the fertilized eggs was carried out by cold shock at 4±1℃ for 15 to 60 minutes starting 4 minutes after insemination at 27℃. The hatching success of cold-shocked eggs was 49.9-69.4%. The triploid character of treated fish was confirmed by karyological and cell size analysis. Triploid ranged from 36.7 to 100% and the incidence of triploidy increased with the treatment time. However the percentage of viable zygotes decreased with increased duration of shock treatment. The chromosome number of the triploid fish was 87, and erythrocyte and their nuclei of triploid were larger in both axes than those of diploid. Triploid fish showed improved growth rate compared to diploid after 6month of age. Histological analysis of the gonads revealed sterility in triploid fish.