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Tuna born from mackerel: Japanese scientists develop surrogate tech to save threatened species

Audrey Akcasu Feb 1, 2015
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Last November the sushi world was struck with some bitter news: the Pacific bluefin tuna was placed on the International Union for Conservation of Nature and Natural Resources’ (IUCN) Red List of Threatened Species. While not considered endangered like its close relatives, the Atlantic and Southern bluefin tuna, it has been proclaimed as a vulnerable species.

Bluefin tuna is considered the best of the best, its tender red meat is coveted by sushi chefs and sushi consumers alike. But what will happen if the Pacific bluefin becomes extinct? Foreseeing a future of sushi connoisseurs being forced to eat tuna-shaped cakes or playing with tuna models to try to get their bluefin fix, scientists have come up with a radical new idea: use mackerel to breed bluefin tuna.

▼ It’s a shame that such a delicious fish has become a threatened species.

If you’ve ever eaten high-quality sushi, there is a good chance you’ve tasted some bluefin tuna. In fact, President Obama faced some flak from Greenpeace after dining at Sukiyabashi Jiro (the restaurant featured in the documentary Jiro Dreams of Sushi) with Japanese Prime Minister Abe. They ate the “special course,” which usually features the famed, but vulnerable, bluefin tuna, much to the displeasure of Greenpeace.

It’s clear that people love to eat bluefin, but apparently they love it a little too much, since overfishing has been a significant factor in the near demise of the species. So what can we do?

▼ Overfishing has caused a lot of problems, but can we reverse it?

While stopping all consumption would be ideal, it might not be enough. Scientists at universities, including Kinki University, have been trying to farm tuna for years, but with little success. One main problem is that tuna take up to five years to mature into the breeding stage of their life-cycle. That’s a pretty long time in the animal world. Not to mention that a full-grown tuna weighs up to 100kg (220lb), and to gain one kilogram they have to eat 20-40kg (44-88lb) of food! Needless to say, they aren’t the easiest guys to take care of. Then there is the problem of the fish being kind of dull in the head, and often killing themselves by ramming into the walls of the tanks, only to be eaten by their cannibalistic brethren.

Tokyo University of Marine Science and Technology fish specialist Goro Yoshizaki has come up with a new, outrageous sounding plan. After years of research with other fish, he will start using mackerel as surrogate parents for bluefin tuna.

▼ This handy diagram makes it a little easier to understand.

It gets kind of technical, so let’s keep it simple. The basic idea is that the scientists will take baby mackerel and inject their reproductive organs with the reproductive cells of the bluefin tuna. As the mackerel mature, the females will produce tuna eggs and the males will produce tuna sperm, instead of mackerel eggs and mackerel sperm. Then, after the normal reproductive affair, little tuna will be born. Hooray!

▼ A baby mackerel being injected with tuna reproductive cells! Cool!

But what’s the advantage of using mackerel? Well, let me tell you! First of all, mackerel aren’t endangered. Better yet, they mature into the reproductive stage within only one year, meaning baby tuna will be born at a rate five-times faster than if we relied on the tuna to make their own babies. Then there is also the benefit of mackerel being significantly smaller (300g), so they are easier to keep in tanks, instead of the open-water reserves that tuna need. Plus, they don’t require as much food, so they are also much cheaper to feed.

▼ It’s funny to think these little guys can birth giant tuna.

Another reason they chose mackerel over other fish, is that mackerel, tuna and bonito are actually all from the same family and sub-family, Scombridae, meaning they have similar DNA, but you would never guess it based on how they taste!

▼ Would you ever stop to think that these sashima pieces are more or less genetic cousins?

While this research seems really promising, it’s going to be quite some time until it’s put into serious action. This summer they plan on starting the first phase of research, but it could be up to ten years before it makes it to the commercial level. The big question now is: How do the mackerel feel about this? In nature, bluefin tuna prey on mackerel, so in a sense, the mackerel are birthing their sworn enemies! Yikes!

▼ If you understand Japanese and want to learn more about the process, check out this video of a lecture by Goro Yoshizaki:

Source: Naver Matome, YouTube (mbsj2013presentations, Goro Yoshizaki)
Images: Wikimedia Commons (OpenCage (edited by RocketNews24), Fisherman, Richard Ling) Prime Time Seafood Inc., Livedoor Blog (Kinisoku)- edited to English by RocketNews24, Screenshot from YouTube (mbsj2013presentations, Goro Yoshizaki), Foodspotting