In the dark green waters off the coast of western Japan, scores of 68kg bluefin tuna glided counterclockwise inside a pen 46m in diameter, the telltale blue streaks on their bodies shimmering just below the surface.
The fish, though, were not just any kind of bluefin tuna, whose fatty flesh is the most prized delicacy at exclusive sushi restaurants in Japan and has set off fishing wars in the world's oceans. They represented the holy grail of fish breeding: bluefin tuna born and raised in captivity.
They were also the lifework of the man shoveling mackerel into the pen from the edge of a boat one recent afternoon, Hidemi Kumai, 71, the head of Kinki University's Fisheries Laboratory. Kumai had spent more than three decades trying to farm the bluefin tuna -- an unusually delicate fish, both physically and psychologically, prone to everything from restlessness to cannibalism -- before succeeding in 2002. Two years later, he began sending it off to sushi counters in Osaka and Tokyo.
"I felt as if I were giving away my daughters in marriage," Kumai said.
When he undertook his quest in 1970, tuna were plentiful in Japanese waters and the Japanese were really the only people interested in eating slices of raw fish. Today, even as the popularity of sushi keeps increasing worldwide, overfishing and pollution have pushed down edible fish stocks.
The competition has become fiercest over the bluefin tuna, which fetches about US$110 a pound at the Tsukiji fish market in Tokyo, the world's biggest. Of the five kinds of tuna eaten in Japan, bluefin accounts for less than 2 percent. But fishermen from New Zealand to Libya comb seas for it; in Croatia, Spain and elsewhere, young bluefin tuna are caught and fattened inside giant underwater cages before being shipped to Japan.
Despite international quotas, the appetite for bluefin tuna is so insatiable that in the Mediterranean it is on the verge of extinction, according to the World Wildlife Fund. To curb quota violations and what the industry calls tuna laundering, Japanese officials have started carrying out DNA tests on imported bluefin tuna.
The Japanese, who eat about 80 percent of the world's bluefin tuna, are now contending with competition from, predictably, the Chinese. As Chinese in Beijing and Shanghai become sushi devotees, they are paying top dollar for bluefin. Some of the best sushi restaurants in Japan are grumbling that bluefin has become too expensive and hard to buy -- and that they might scratch tuna from their menus instead of suffering the indignity of serving the cheap stuff.
There is a "high possibility," Kumai said, that in a decade or two, as China keeps getting richer, Japan may simply be priced out of a shrinking bluefin market.
"Now only Chinese in the coastal areas are eating sushi or can afford to," Kumai said. "What happens when the Chinese in the vast hinterland start eating sushi?"
As part of Japan's national interest, and also because the Japanese have been exhausting the world's tuna stocks, Kumai advocated the large-scale farming of bluefin tuna, led by the government.
"This has to be a national project," he said. "Now Americans and Chinese are eating sushi, so we can't just sit back."
The outside threat has added urgency to Kumai's work, one that he had never imagined when he began fish farming in the late 1950s. As a boy growing up in the landlocked prefecture of Nagano, he had longed to see the ocean, but World War II restricted travel. When he finally caught a glimpse of the sea during a junior high school trip, he was hooked.