It is no denying fact that the succulent flesh of ‘king of sushi’ is prized by dinners at high-class restaurants from Tokyo to London and New York. This has increased the demand for bluefin tuna and as a result the stock of the species is on the verge of extinction. The conservation group WWF has warned that Mediterranean bluefin tuna stocks were on the verge of collapse, and the breeding population just three years from extinction, as a result of overfishing.
Growing demand of tuna in Japan, and increasingly the U.S., Europe and China, is decimating stocks among the world’s four bluefin populations. It is said that several attempts at imposing ambitious quotas have had little impact. Although fisheries from several countries agreed on new bluefin quotas late last year, they were still some 47 percent higher than the levels recommended by their own scientists — a political fudge that environmental groups condemned as a “disgrace.”
Japan has the highest consumption of tuna but it may also offer the key to the species’ survival, thanks to a team of researchers working out of a laboratory in Tokyo. The team’s leader, Goro Yoshizaki, a professor at Tokyo University of Marine Science and Technology, has perfected a method of assisted reproduction in which sperm and ovaries from donor trout are implanted in salmon recipients.
It is told that when the salmon reach maturity and mate, they produce a large number of hybrids, but also a smaller number of pure trout. Last year his work reached a critical point when he identified the presence of sperm of a nibe croaker in the testes of a mackerel, saltwater fish that have physiological similarities to tuna.
Yoshizaki is trying all way to save the imperiled bluefin. He believes he is only a few years away from adapting the technology to enable him to transplant sperm and ovary stem cells from bluefin tuna to mackerel, and for the recipient mackerel, when mature, to produce a precious bounty of bluefin sperm and eggs. But the main hurdle is obtaining enough stem cells from bluefin testes to produce both eggs and sperm. Preliminary experiments have proved unsuccessful, but the professor is certain he is close to a breakthrough.
