Even so, demand for bluefin sushi is so intense that others say the tuna will inevitably follow salmon, catfish and other smaller fish into successful commercial aquaculture.
"I think that about 10 years from now, we'll get bluefin tuna to breed via land-based hatcheries," said Yonathan Zohar, the director of the University of Maryland Center of Marine Biotechnology. "It's only a matter of time and resources."
The first problem to surmount is bluefin behavior. Bluefin can take up to 12 years to reach sexual maturity, compared to about three years for catfish, and getting them to breed outside their natural habitat is difficult. Life in a floating sea cage or giant tank apparently does not provide the right environmental cues to tell the fish to turn on those sex hormones and produce another generation.
A European Union project recently made a start at clearing these hurdles. Zohar collaborated on the paper, published in the July 2007 issue of Reviews in Fisheries Science, which used drug implants to get bluefin to produce fertilized eggs in captivity. In the future, this technique may help scientists overcome the practical and financial barriers to bluefin farming by making the tuna breed at a younger age.
Zohar compares his research to a gynecology practice for fish. The captive tuna's brains were not producing enough of the hormones that normally tell the fish's bodies to breed, so Zohar developed a drug treatment that mimics the hormone at the top of the chain of command: gonadotropin-releasing hormone.
Some scientists are skeptical about the prospects of breeding bluefin, and environmentalists say the breeding efforts are a costly distraction. "That's a really expensive way of not solving a problem — which is the overfishing of bluefin tuna," said Tom Grasso, the director of marine conservation policy at WWF, a conservation organization that currently supports a worldwide ban on all Atlantic bluefin fishing and encourages people to eat other kinds of tuna instead.
The bluefin population of the western Atlantic has plunged by more than 90 percent since the 1970s, according to the International Commission for the Conservation of Atlantic Tunas. Last year, American fishermen brought in less than 15 percent of their allowed catch.
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