Optimization of cold-shock conditions for the induction of triploidy in the Pacific bluefin tuna, Thunnus orientalis (Temminck et Schlegel)

Abstract Pacific bluefin tuna (Thunnus orientalis) is one of the most important species for aquaculture in Japan. In recent years, the reduction in muscle fat content during sexual maturation in farmed T. orientalis has become a serious problem. Herein, as a first step toward sterilization to avoid the deterioration of flesh quality associated with sexual maturation, we examined cold-shock conditions for inducing triploidy in T. orientalis. In this study, three treatment variables (initiation timing, duration, and water temperature of the cold-shock treatment) were considered, using the fertilized eggs collected immediately after spontaneous spawning in a land-based tank. We found that the optimal cold-shock conditions for T. orientalis were 5 °C for 15 min starting from 5 min after fertilization. Under these optimal conditions, we obtained high triploidization (96.6 ± 3.3%) and total hatching (64.5 ± 8.7%) rates. Therefore, using eggs obtained by spontaneous spawning in a land-based tank and the triploidization method established in this study, it is possible to repeatedly and efficiently produce triploid T. orientalis. Statement of relevance In recent years, deterioration of flesh quality associated with sexual maturation in aquaculture-produced Pacific bluefin tuna (PBT) has become a serious problem. To avoid this problem by sterilization technique, in this study, we have developed an efficient method for the induction of triploidy in PBT, using the fertilized eggs collected immediately after the spontaneous spawning in a land-based tank. We believed that the results of present study are a valuable first step toward the sterilization of PBT.