The research on artificial hatching and breeding of juvenile bluefin tuna started in 1979. Initially, we were not able to raise the fish to the length beyond 10 centimeters. The experiment was discontinued temporarily, but in our efforts to raise juveniles in 1994 and afterwards, the way was opened toward establishing the technology for breeding the tuna for the period after the juvenile stage.In 1994, only 43 tunas of age 70 days (body length of 20 centimeters) were obtained out of 2.64 million fertilized eggs, with the survival rate standing at 0.0016%. The results of breeding at that time clarified (1) initial decrease until age of 10 days; (2) cannibalism around the age 10-30 days; and (3) the fact that collision deaths that followed in about one month and the three major decrease periods occur continuously. Since then, development of technology on reducing the decrease has been advanced.
At present, the survival rate in seed production stands at around 3% in the land-based aquariums, and about 30% in the intermediate breeding period after the fish are moved to the ocean pens—which is a drastic improvement over 15 years ago. However, the survival rate for the whole period of farming still remains at around 1%, a level conspicuously lower compared with 60-70% for red sea bream and 20-30% for amberjack. For all that, it is safe to say that the commercialization of full-scale farmed bluefin tuna has finally come within the range of realization. Expansion of farming facilities and cooperation with other related organizations are considered indispensable for the further expansion of production, Prof. Miyashita said.