LINDA WERTHEIMER, HOST:
At this moment in a windowless laboratory in downtown Baltimore, some tiny, translucent fish larvae are swimming around in glass-walled tanks. They are baby bluefin tuna. Scientists there are trying to grasp what they call the holy grail of aquaculture: raising this powerful fish, so prized by sushi lovers, entirely in captivity. They're reporting successes, but many hurdles remain. NPR's Dan Charles reports.
DAN CHARLES, BYLINE: I couldn't see the larvae at first. Yoni Zohar, the scientist in charge of this project, had to point them out to me.
YONI ZOHAR: You can look; they are very hard to see. They are like small speckles in the water. But you see them beautifully here swimming.
CHARLES: They look incredibly fragile and helpless, just drifting in the water currents in 90 gallon tanks. But they're already gobbling up microscopic marine animals, which in turn are living on algae.
ZOHAR: I mean, it's amazing. We cannot stop looking at them. I mean, we are really sitting here around the clock and we are looking at them because it's so beautiful.
CHARLES: Beautiful because they're rare. Scientists are trying to raise bluefin tuna completely in captivity in just a few places around the world. This experiment at the University of Maryland Baltimore County's Institute of Marine and Environmental Technology is the first successful attempt in North America. At least it's a little bit successful - most of the larvae have died, but hundreds have survived for 10 days.
ZOHAR: And we are counting every day. We want to be at, like, 25 to 30 days.
CHARLES: Because this is the time when they typically don't survive?
ZOHAR: This is the bottleneck. You know, the bottleneck is the first three to four weeks.
CHARLES: If they make it, they'll be juvenile fish and much more sturdy. What they need then is lots to eat. Fully grown, the bluefin tuna is a tiger of the ocean, powerful and voracious. Its flesh is in high demand for sushi all around the world. Journalist Paul Greenberg wrote about the bluefin tuna in his book "Four Fish." He says if you're an angler, catching one is an experience you don't forget.
PAUL GREENBERG: When they come onboard, it's just this - it's like raw energy coming onto the boat. Their tail will go bop, bop, bop, bop, bop - it's like this outboard engine that's just blazing with power and energy.
CHARLES: The fish can swim 45 miles an hour, across entire oceans. And they're valuable - demand for them has grown especially in Japan, where people sometimes pay fantastic prices for them. It's led to overfishing and now wild populations of tuna are declining. That's why scientists like Yoni Zohar are trying to invent a new way to supply the world's demand, bluefin tuna farming.
ZOHAR: The vision is to have huge tanks, you know, land-based, in a facility like you see here, having bluefin tuna that are spawning year-round, on demand, producing millions of eggs.
CHARLES: And those eggs would hatch and grow into full-grown fish, a plentiful supply of tuna, which brings us back to these precious larvae. Before there can be aquaculture, these larvae have to survive. Here in the laboratory, they're tinkering with lots of things to make that possible - the lights above the tanks, the concentration of algae, water currents to keep the fragile larvae from sinking toward the bottom of the tank.
ZOHAR: They tend to go down. They have heavy heads - they go head down and tail up. If they go to the bottom, they hit their head on the bottom, they're gone. They're not going to survive.
CHARLES: Enough are surviving that Zohar thinks they're getting close to overcoming this obstacle. But that still leaves a final hurdle, figuring out how to satisfy the tuna's amazing appetite without causing even more damage to the environment. A tuna's natural diet is other fish - a lot of them. Right now, you have to feed tuna something like 15 pounds of fish like sardines or mackerel to gain a pound of consumable tuna. So you could cause a lot of damage to those species to keep the farmed tuna alive. Yoni Zohar thinks it will be possible to reduce this ratio or create non-fishy tuna food. But Paul Greenberg, the journalist, says this basic fact about tuna really does make him wonder whether tuna farming is the right way to go. You'd be increasing the population of a predator species that demands lots of food itself.
GREENBERG: I mean, why would you want to domesticate a tiger when you could domesticate a cow?
CHARLES: Or even better, a chicken, which turns just two pounds of vegetarian feed into a pound of meat. Greenberg says if farmed tuna really reduces the demand for tuna caught in the wild, that's good. But it might do more good, he says, to eat a little lower on the marine food-chain. We could eat more muscles or sardines - let more tuna roam free. Dan Charles, NPR News.