The prospect is tempting: An innovative new business for the Big Island, producing a product high in demand but difficult to obtain, using state-of-the-art technology to protect the environment.

That's the promise held out by Hawaii Oceanic Technology Inc., which proposes to raise sashimi-grade bigeye and yellowfin tuna, from eggs to plate, in giant cages in deep waters off Kawaihae.

With 12 cages and 12 million pounds harvested each year, it would be the largest open-ocean fish farm in the state.

But even with the release of an environmental impact statement last week — a major step forward — the large size and experimental nature of the project demands that state regulators, and the public, keep a critical eye on the project as it moves forward.

Critics of open-ocean fish farming say that controlling the rapid spread of disease among fish in close quarters is one of the most serious problems with the industry. So is developing breeding methods that don't create weaker, genetically inferior fish — a problem that could infect hardier wild populations if farmed fish escape their pens.

Hawaii Oceanic hopes to avoid such problems by developing better breeding techniques, a sustainable organic feed and a new type of storm and shark-proof underwater cage. "This is sort of a giant demonstration project," says company CEO Bill Spencer. The objective: an organic, ecologically sustainable fish.

It's a worthy goal. Aquaculture is growing rapidly as heavy demand decimates wild fish stocks. But as an industry, aquaculture still in its early stages. The development and promotion of ecologically friendly techniques — akin to organic agriculture on land — should guide the industry's growth, especially when it's in the open ocean.

Whether Hawaii Oceanic's 'ahi cages can meet those environmental standards has yet to be proven. It must still get a state permit and enough investment capital to move forward. But if given the chance to make its case in the ocean, it should be held to its promises.