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'Ranching' tuna the eco-friendly way

By Kyung Lah, CNN
  • Bluefin tuna farm off coast of Japan rears fish from hatchlings to fully grown
  • Beloved by sushi aficionados, wild bluefin tuna have become endangered
  • "Closed system" of the tuna farm in Kushimoto, Japan, could be sustainable solution
  • Farming does rely on large quantities of mackerel to feed tuna, critics say

Kushimoto, Japan (CNN) -- Tokihiko Okada has hundreds of children. Well, not literally, but you might as well call the giant bluefin tuna he cares for in the ocean tanks his "children."

Okada is the general manager at Kinki University's Fish Nursery Center. He started working with the university's researchers after leaving college more than 20 years ago.

In that time, he's seen monumental change in the attempts to farm tuna. Kinki University boasts a farming program that may help stem the steep decline of the world's bluefin population.

There are many bluefin farms around the world, known as tuna "ranching." Fish farmers capture bluefin juveniles in the wild and raise them to maturity before shipping them to market, rather than fishing for them in the open ocean.

Video: Japan's greener tuna
Video: Going deep for the shot

But what's different about Kinki University's program is that it's a closed farming system, which means that the bluefin tuna raised in their ocean tanks have never been in the wild.

They're produced from hatched eggs, raised, and then fished for consumption.

It's one of the few programs on the globe to successfully raise the delicate bluefin tuna.

For three generations, Okada has helped successfully raise bluefin tuna for the world's gourmet restaurants.

"This is the first pond worldwide made in 2002 that contains completely farm-raised tuna," Okada told CNN, standing above the giant tank off of the western shores of Japan.

The tank is filled with 34 tuna, a group Okada feels especially close to.

"They're seven years old now. They've been breeding eggs every year for three years now. Compared to the other fish farms, we were off to a slow start. But we've been doing this closed system for three generations now, and they've been a success. We don't have to use wild tuna anymore, because we can raise our own," he said.

CNN joined Okada as we visited a dozen different tanks at the Kinki University site in Kushimoto, Japan. We stopped at a large tank filled with three-year-old tuna, where fishermen would be pulling out seven tuna on this day.

We have to leave nature intact because if we take too much from it, we won't be able to eat wild tuna.
--Tokihiko Okada, Kinki University Fish Nursery Center

Each of the tuna has been specifically ordered by a restaurant, some as far away as the United States.

The fishing is easy. The fishermen toss a mackerel on a hook and pull out a bluefin in just minutes. The fish is beautiful; glistening blue and silver with a yellow fin on its spine. The fishermen zap the fish in the brain with an electric rod, stunning it. It only takes a few minutes to clean it and ice it.

The bluefin is prized for its buttery flesh, revered by sushi aficionados for its taste and restaurants for its high price. It's why the wild bluefin population has plummeted worldwide.

The WWF predicts Mediterranean bluefin will be wiped out by 2012 because of overfishing to sate the appetite of gourmet diners.

"We have to leave nature intact," said Okada, "because if we take too much from it, we won't be able to eat wild tuna. They'll be gone."

The Kinki University bluefin are not completely eco-friendly.

Tuna eat a massive amount, approximately 10 percent of their weight per day. The fish are fed wild mackerel by the truckload. Hardly eco-friendly, say critics. Greenpeace says a far better solution is to educate the diner and get them to stop eating bluefin tuna.

That won't work, says Okada, who points out there's a multi-billion dollar worldwide market for tuna. Okada says the university is working on a vegetable protein to feed their farmed tuna to make it a greener choice.

"I think it's very difficult for people to stop eating bluefin tuna completely. We should be balanced in our solution."