Sakana Dream (Tateyama City, Chiba Prefecture) is developing and marketing new cultured fish by applying a surrogate fish parent technique that transplants reproductive stem cells between different species. The technology is based on that of Professor Goro Yoshizaki of the Tokyo University of Marine Science and Technology, who is known for his “research on making mackerel give birth to tuna”. Reproductive stem cells from fish that take a long time to mature sexually or are technically difficult to mature sexually in aquaculture are transplanted into a fish of a different species that can more easily spawn, and eggs and sperm are produced and fertilized to produce young fish. When some cells are removed from the gonads of the donor fish and transplanted into the abdominal cavity of the young host fish, the reproductive stem cells of the donor fish escape immune rejection, migrate to and live in the gonads of the host, mature as the host grows, and produce eggs and sperm of the donor fish. Furthermore, if a fish with the sterility trait is used as a host, it can be made to produce only donor-derived germ cells instead of host-derived germ cells. Professor Yoshizaki aims to apply this technology to research applications such as increasing the number of bluefin tuna seedlings by having mackerel lay bluefin tuna eggs. So far, he has succeeded in inducing rainbow trout to lay landlocked salmon eggs and char, and kusafugu to lay tiger puffer fish eggs. In addition, Professor Yoshizaki and his colleagues have established a technique for transplanting reproductive stem cells  from dead fish. In a study using rainbow trout, germline stem cells taken from individuals that had been dead for 12 to 24 hours were viable in the host fish.

Sakana Dream is committed to selling farmed fish with high added value in terms of taste and nutritional value. In addition to live fish, the company is also using technology that allows fish of different species to lay eggs by transplanting germline stem cells from fresh fish that have just died, as well as technology that crossbreeds fish to produce fish with different traits. Sakana Dream is attempting to commercialize the kaiware, a tasty fish for which cultivation technology has not yet been established, by having farmed fish of a different species lay eggs. Kaiwari is a saltwater fish belonging to the horse mackerel family of the sea bass order, also known as flathead flounder, and adults are about 20 to 30 cm in length.