Sat, Sep 30, 2006 - Page 9 News List

The holy grail of fish breeding

The farming of bluefin tuna, a delicacy at sushi restaurants, may have been developed in the nick of time as wild stocks come under increasing pressure


Over the years, the university's Fisheries Laboratory was first in the captive breeding of about 20 fish species, including halibut, flat bream and Japanese amberjack. Much of the work went on in the placid Pacific waters between the town of Kushimoto and the small island of Oshima, where various fish are farmed inside pens.

But bluefin are the main attraction. At first, capturing young bluefin in the wild and transporting them into pens proved difficult, with most of them dying in fishermen's nets. Bluefin bruise easily because of their delicate scales, and their gills take in little oxygen compared to other fish, so they have to swim continuously to breathe -- even while asleep.

Cooped up, many died quickly. Eventually, Kumai learned how to keep them alive and scored a first in 1979 when the fish spawned inside a pen. Still, after hatching, the fry died after a few weeks -- a cycle that went on until 1982, when the fish inexplicably stopped spawning.

They resumed in 1994, but new problems arose. The fry survived, but the bigger ones kept gobbling up their little brethren.

"Other fish, the sea bream or flatfish, do that, too," Kumai said. "But tuna are very aggressive. The population could shrink to a third overnight."

Kumai scooped the fry into bowls -- their delicate bodies would chafe at nets -- and segregated them by size. Unlike other species, they quickly grew tails but lagged behind in developing other fins -- so that they could advance but not turn.

"They kept crashing into nets and dying," Kumai said with a grave face. "We took X-rays and found their necks were broken."

For fish that can grow to be as large as 800kg, they are also unusually sensitive. Fireworks, even the headlight of a car, can cause them to panic, crash into nets and break their necks.

Nevertheless, many survived and spawned eggs. In 2002, these eggs hatched and the fry survived. By segregating the fry from the larger fish, raising them in bigger pens and adjusting the water temperature and their diet through trial-and-error experiments over the years, he was able to raise them to adulthood. In 2004, these fully farmed bluefin tuna were sold to an expectant nation.

"I've never met anyone who told me it tastes bad, though I know it's hard to say that to my face," said Kumai, who said he had never eaten wild bluefin.

Some sushi chefs in Kushimoto sniff at the ranched bluefin, saying it yields a fatty meat that does not taste as good as the wild variety. Wild bluefin, migrating across oceans, tend to be lean. But Kumai's couch potatoes are 10 percent lean and 90 percent fatty.

Because of decreasing stocks, Kumai's bluefin is now sold only once a month at a Mitsukoshi department store in Tokyo -- for a third less than the wild kind. That fact annoyed Kumai.

"Just because it's farmed, the prices are automatically lower," he said. "If it's good, it's good. There shouldn't be a difference."

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