(Fortune Magazine) -- Neil Sims is standing on the deck of a 35-foot feed boat off the coast of Kona, Hawaii, staring at a dorsal fin slicing through the calm morning sea below. For the past hour we've been snorkeling around the submersible cages owned by his aquaculture company, Kona Blue Water Farms. The nets house nearly half a million fish, a species of yellowtail known as Kona Kampachi.

As we dawdled in the 200-foot-deep water, three bottle-nosed dolphins played around us like schoolchildren at a zoo. Now we're watching a crew siphon food pellets into the cages. But the dorsal fin has everyone distracted. It doesn't belong to a dolphin. Sims has heard there's been a hungry tiger shark hanging around at feeding time. This leaves no doubt. "Do you fellas have a boat hook?" he asks in an Australian drawl that still runs thick after 18 years on the Big Island.

A boat hook - it should be defined for the nautically challenged - is little more than a curtain rod with a plastic "J" on the end. It's used mainly to grab a small buoy when docking. There's no sensible reason for Sims to want such a device now. We're half a mile from shore and 400 yards from our own vessel. He arches an eyebrow in my direction. "So," he asks, "you wanna swim for it?"

If ever there were a man who could stave off a man-eating shark with a curtain rod in a mad 400-yard swim for safety, Sims would be the one. It wouldn't even be the biggest problem he's trying to single-handedly tackle today. For example, the plight of the commercial fishing industry.

Let's back up a bit. Our oceans are being drained of food. Doctors tell us to eat more fish; it's good for the brain and good for the heart. We yearn for our weekly sushi fix. And increasingly so do our friends in China, India, and elsewhere in the developing world.

To meet this growing appetite, commercial fishermen are scooping up everything that's edible (and a lot of what's not). Couple that trend with the effects of global warming, and the situation has become so dire that some scientists think seafood stocks will totally collapse by 2048.

If that sounds sensationalistic, consider that the once-abundant cod off New England are already gone. The same is happening on the West Coast. King salmon off California and Oregon are at the lowest level in history; there will probably be no fishing season this year.

Equally alarming, many of the tuna, swordfish, and other species high up on the food chain are so laden with mercury (cast off mainly from coal-fired energy plants) that eating them is dangerous for children and pregnant women.

Aquaculture would seem the answer, but it has its own problems. Farmed fish- especially carnivorous finfish like salmon - tend to lack the flavor of their wild counterparts, can be lower in nutrients, and are often dyed to appear edible. The farms themselves, being monocultures, can be havens for disease, so they are sometimes infused with prophylactic antibiotics. Those chemicals and the concentration of feces make poorly monitored shoreline farms devastating to the environment.

Ravaged marine life

Sims has a better way. He wants to satiate our appetites without poisoning us or the environment. "We would have never been able to sustain our population if we had remained a hunter-gatherer society on land. And I'm not sure what makes people think we can remain that way in the ocean," says the 49-year-old marine biologist.

A former fisheries researcher in the Cook Islands, Sims was disgusted by how locals ravaged marine life there. But the scene also inspired his idea for a new (patents pending) style of deepwater fish farming. "We're finding new ways not just to grow more fish - we're trying to grow more fish better," he says.

So just what is Kona Kampachi? Think of it as a more versatile cousin of hamachi. It's not genetically engineered in any way, just well bred. It's sashimi-grade and sustainably farmed without hormones or prophylactic antibiotics. It's richer in omega-3 than just about anything else in the ocean and has no detectable mercury. It melts on your tongue, holds up on the grill, and is so rich in oils that it'll fry in a pan without butter.

Pregnant women, nursing moms, young children: Eat as much as you want of what might just be the best-tasting fish you've ever had. Really. It's that good.

Kona Blue calls its designer yellowtail the "fish of the future." In truth, it's more like a fish of the past. After all, sea life wasn't always scarce or poisonous. But the cultivation does involve scientific and technological advancements. The most obvious example is the sea station. Sims helped modify submersible pens to make them flippable and therefore more easily cleaned. Every few weeks a net is raised, turned over, scrubbed, and dried in the Hawaiian sunshine. The company also regularly takes water and seabed samples beneath the pens and at various control sites, records the process with webcams, and posts the data and video online.