Cold-shock induction of triploidy in the Japanese jack mackerel (Trachurus japonicus)

Abstract In this study, we induced triploidy in the Japanese jack mackerel ( Trachurus japonicus ), an important species in Japanese fisheries, through cold-shock treatment, and evaluated the sterility of the resulting triploids. Eggs and sperm collected from wild-caught adults were fertilized, and the fertilized eggs were used to optimize two treatment variables: water temperature and duration of the cold-shock treatment. Based on the proportion of normally developed triploids that hatched from the eggs treated 4 min after fertilization, the most effective cold-shock conditions were 0 °C (65.0% ± 19.1%) and 4 °C (63.4% ± 9.7%) for 5 min. Triploid fish were reared to adulthood, and their gonadal maturation was compared with that of control diploids. Histological examination of control diploids during the spawning season at 1 and 2 years of age showed normal vitellogenesis in the ovaries and abundant sperm production in the testes. Conversely, the gonads of triploids were underdeveloped, with no vitellogenesis in the ovaries, and no spermiation was observed in males. These findings indicate that oogenesis and spermatogenesis are disrupted in triploid T. japonicus , suggesting that triploidization is an effective method for inducing sterility in this species.