Research Challenge

Tuna is now declining to the point of being listed as an endangered species. The two solutions to this problem are "aquaculture" and "propagation.
Aquaculture" is an artificial method of increasing the number of tuna by managing the entire cycle of raising eggs, turning them into adult fish, and spawning the next generation of eggs. Propagation involves keeping the parent fish and releasing the fry that hatch from the eggs until they are large enough to survive in the wild, both of which are already being done in Japan.
The "propagation" business is becoming one of the pillars of Japan's fisheries, with the salmon fisheries of Hokkaido and Tohoku and the scallop fisheries of Mutsu Bay in Aomori Prefecture being particularly well-known. The idea of using tuna in this way has been difficult due to the size of the tuna's parents and the length of time it takes to raise them.

As a breakthrough, the idea at the beginning of this paper was conceived to use mackerel as a surrogate parent for tuna. The first step is to find the cells that will become the source of tuna eggs and sperm. The next step is to transplant these cells into both male and female mackerel pups. Hatchlings are the technical term for baby fish, which grow through the following steps: eggs, hatchlings, fry, and juveniles. Thereafter, these mackerel continue to produce tuna eggs and sperm as they grow. The strategy is to fertilize the eggs and sperm produced by these mackerel to produce tuna. Professor Yoshizaki of Tokyo University of Marine Science and Technology focused on primordial germ cells, which are the source of eggs and sperm, in conducting this experiment, and as a result of his research, he succeeded in producing rainbow trout from landlocked salmon.