Prized sashimi tuna bred in captivity for first time

"And on that farm he had a?" ? tuna? Aquatic Old MacDonalds have moved a stride closer to fully farming bluefin tuna now that all three species of the fish ? one of the most endangered of those commercially fished ? have produced eggs and larvae in captivity.

Umami Sustainable Seafood of San Diego, California, announced that it has definitive proof from DNA maternity tests that eggs and larvae collected from its research and production facility in Croatia came from around 1000 captive northern bluefin tuna grown to maturity over the past five years.

This is the first time that the endangered species ? highly prized for sashimi dishes ? has spawned in captivity.

The next step for the company is to demonstrate that the larvae can be grown into fully mature fish, completing the entire growth cycle in captivity.

Proof that the fish produce eggs and larvae in captivity is a significant advance, however. "The biggest milestone for us was the massive spawning we had this year, with billions of eggs released," says Oli Steindorsson, the chief executive of Umami.

Young and wild

Umami already farms northern bluefin, but at present the company replaces harvested fish with young caught fish. It aims to end this practice once replacements can be grown "on the farm". "Reducing the need for wild capture of juvenile fish and instead being able to breed bluefin tuna in captivity addresses one of the issues needed to move towards more sustainable aquaculture," says Sebastian Troeng, vice-president of the global marine division at the US environmental group Conservation International.

To boost bluefin numbers in the wild as part of its hatchery project, Umami will deposit most of the eggs in the sea, but will be retaining some eggs and larvae for further experiments.

The breakthrough means that all three species of bluefin have now been bred in captivity. Kinki University in Kushimoto-cho, Japan, successfully bred Pacific bluefin in 2007. And in 2009, Clean Seas, a company based in Port Lincoln, South Australia, managed to breed southern bluefin tuna, the most endangered of the three bluefin species.

Steindorsson told New Scientist that globally, around 50,000 tonnes of bluefin tuna meat is consumed per year, sourced equally between farming and fishing. Of the 25,000 tonnes of farmed fish, Umami is the largest single supplier, producing 2500 to 3500 tonnes of sashimi-grade bluefin each year. The balance comes from around 40 much smaller suppliers in the Mediterranean, Japan and Australia.

Umami grows the bluefin in pens 50 metres in diameter and 30 metres deep, separated from the open sea by robust fortified nets. "They are protected from predators and they don't escape," says Steindorsson.

Big eaters

Troeng says it is still up for debate whether such fish farming is truly sustainable, though. The fish receive feed containing sardines, herring, anchovies or mackerel. "A major and remaining challenge is to improve the feed conversion ratio, as bluefin tuna in captivity require around 20 times more fish for feed than what is produced," he says.

But recently, Conservation International broadly backed seafood farming in a report on its global effects and sustainability. It noted that farming is now expanding rapidly: in 2009, for the first time, more seafood was farmed than caught in the wild.

The organisation also issued a report last month warning of the plight of bluefin tuna, and calling for increased protection for all three species, which it said are "susceptible to collapse under continue excessive fishing pressure".

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