Japan Today

Holy mackerel: A breakthrough in tuna science?

By Justin McCurry

The next time you dine at a Japanese restaurant, try to steer clear of the tuna sashimi. If you're unable to resist the temptation — and, let's face it how many of us can? — make sure you savor every last slice. In just a few years, it may have disappeared from the menu for good.

Our appetite for the undisputed “king of sushi,” whose succulent flesh is prized by diners at high-class restaurants from Tokyo to London and New York, is far from being sated.

Only last week the conservation group WWF 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 and a failure to curb our desire for melt-in-the mouth otoro.

Demand in Japan, and increasingly the U.S., Europe and China, is decimating stocks among the world’s four bluefin populations. The number of Mediterranean bluefin, for example, has more than halved since the 1950s.

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% higher than the levels recommended by their own scientists — a political fudge that environmental groups condemned as a “disgrace.”

While Japan is often cast as the villain of the piece for its voracious consumption of bluefin, 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. 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.

Now Yoshizaki is in a race against time 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.

The biggest obstacle 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.

Success, he says, depends on his ability to exploit the sexual bipotency of enriched stem cells from bluefin to produce both sperm and ovaries in mackerel.

“The hypothesis is that the bluefin tuna has some stem cells in its testes, but that the concentration is very low,” he tells GlobalPost. “If that’s the case, and we can find a way to enrich them, then we should be able to repeat the success we had with the salmon and trout.”

Replicated on a big enough scale, the process could produce masses of tuna fry with enough genetic variation to survive and multiply in open sea after being raised in marine ranches, thereby helping replenish stocks of wild fish.

The approach has several advantages over the bluefin farming pioneered by Kinki University in western Japan, in which the sperm and eggs from farm-raised tuna are used to create test-tube fish, which in turn are reared for about four years in offshore pens until they are big enough to be sold.

The process is time-consuming and costly, and, aficionados insist, produces sashimi of an inferior quality.

The Japanese government, aware of mounting international criticism of its failure to rein in fishermen, have given Yoshizaki’s team a 300 million yen grant for the five-year project.

They have three years left to produce results. “In that time I want to produce at least one tuna bred using surrogate mackerel,” Yoshizaki says.

“And if I’m being optimistic, we should have all of the techniques we need to mass produce tuna through surrogate mackerel in less than 10 years. If we can make it work in conjunction with marine ranching, then we can ensure there will be a healthy population of bluefin tuna forever.”

The professor is almost evangelical in his enthusiasm for his work, but he also feels a heavy moral responsibility to succeed. “Japanese people consume a lot of tuna so it is up to us to do something to save this precious ocean resource.”

In the meantime, the bluefin tuna’s hopes of staving off extinction partly rest with consumers. Several sushi and supermarket chains have stopped selling it, while diners can refer to a selection of new ethical eating guides telling them exactly what and what not to order over the sushi counter. Needless to say, bluefin is a definite no-no.

© GlobalPost

©2024 GPlusMedia Inc.

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When overseas (especially Chinese) buyers purchase tuna in Tsukiji, does the fish get counted as having been consumed in Japan?

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Yoshishaki-san better spend the Y300m pretty quick, before the Japanese government stumbles on this article...


Last month Cleanseas Tuna (aquaculture outfit in Australia) reported 'over 50 million fertilised eggs and 30 million larvae were produced'.

Maybe Yoshishaki-sancan take his team out for a slap-up sushi dinner.

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Great, GM fish. We shouldn't take this route. Look at what happened to the native fish when the emperor decided to chuck some Black Bass into the Biwako.

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Why does this read as "fun fun" tuna as we know it is gone in 3 years?

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when you consider the hoo-ha about whale hunting it makes me wonder what will happen in a few years when tuna stocks get dangerously low and some kind of international ban has to be enacted. scientific research tuna sashimi, anyone?

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Yellow fin tuna is by far, better tasting than blue fin tuna.

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nice one jonnyboy :)

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I love Otoro. It should be international law that only people living in Japan can eat Tuna.

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They should make a new law regarding how tuna is caught. Right now whole schools of tuna are caught and fattened in their cages leaving hardly any survivors. Not only that, quotas are almost always exceeded and in Italy, the mafia control the fishing.


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I am prepared to do research here in Australia if the Japanese Government will extend me 300 million yen over five years. I will get the scientists currently feasting on the "man made global warming" bandwagon to switch as increasing numbers of the world's population see it as a giant research grant hoax. We can then all share the faith in saving the wild Bluefin Tuna from massive overfishing. When that fails we can find another faith based scientific research project. These guys have to eat to - in any case would you prefer the money was spent on assisting hard up Japanese deserted wives or the unemployed. I am with Peta D 78 - why do it when a Japanese University and a South Australian company have already successfully done it.

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looks like some scientific research ships will be needed for real research this time

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A breakthrough? Nice science in this case but the real breakthrough for the future of tuna would be in reducing the eating, even going so far as to honouring a quota.

This is a worldwide problem and if Japan could take the lead in presenting it to the world as such, maybe some action can happen. Japan being a large per capita fish eater would go a long way to legitimize the concerns.

But waiting for technology to save us from ourselves seems like a never ending scenario. Have we no will?

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sf2k. I think you may be right. If Japan, recognized as the world's No.1 fish eating nation would take on the role of bringing honesty, facts, science about fishing throughout the world and took the honest broker leadership role to sort out the massive overfishing problem the world would cheer. It is about time the Japanese came out of their bunkers and shed their WW11 cringe and realized the world wants them to take leadership roles in world affairs and for a start use their resources to lead the world to clean up fishing, they would gain enormous respect.

Every time I look at a nature show to see that cod were fished out in Nova Scotia or sardines were fished out in California or foreign fishing vessels were vacuuming at night all the fish from the coast of Somalia leading to the Somali piracy exploits now, one thinks who is going to show some real leadership. My question then is, are the Japanese up to it? Common Japan, the world needs you.

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Japanese government pay attention here - Brunobear has his(her) hand out for the Y300m - I will do the job for 80% of whatever Brunobear offers (down to a minimum of 320yen)

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PeterD 78: I'm a his. I am prepared to let this opportunity pass if the Japanese would take on an honest leadership role in world fishing and whaling. They could spend the 300 million Yen on it as a start.

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