BALTIMORE - In Maryland, Professor Yonathan Zohar is considered a genuine environmental hero, thanks to a successful project to return the blue crab to Chesapeake Bay, whence it had nearly disappeared due to overfishing. And at a conference in Eilat next week, Zohar will present a project likely to interest many Israelis: fish farming on land, at a reasonable cost and with no environmental pollution. Fish farms located in the Gulf of Eilat have become highly controversial in recent years, due to claims that they pollute the Gulf, and as a result of a recent government decision, removal of these farms has begun.

Zohar, a graduate of Hebrew University, previously held jobs both at Eilat's Institute for Marine Sciences and with a company that farms fish in the Gulf of Eilat. Today, he heads the Center of Marine Biotechnology at the University of Maryland, and he is one of the organizers of next week's international conference on marine biotechnology.

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Zohar believes fish farming will gradually migrate to land worldwide. His prototype, located at the university, is a tank containing many hundreds of sea bream - the same fish bred in the Gulf of Eilat farms.

The fish are raised in complete isolation from the natural world. Zohar "manufactures" his seawater out of tap water that undergoes special processing. The payoff is that, instead of polluting the sea, the pollutants manufactured by fish farms do not pollute at all: The polluted water is piped to another container, where the pollutants are then eaten by specialized bacteria. The water is recycled into the fish farm.

The fish spend nine months in the tanks, during which time the water never needs to be changed, since the bacteria purify it. The pollutants eaten by the bacteria are released into the air as methane gas, and this gas is then trapped and converted into energy used to power the system.

Zohar's system also has another advantage: Fish bred in the open sea not only pollute, they also absorb pollutants from their surroundings. By contrast, Zohar's fish are virtually pollutant-free.

The system's main disadvantage is cost: It is obviously cheaper to breed fish in the sea. However, Zohar says, this disadvantage is steadily disappearing as regulators impose more and more demands on sea-based fish farms. For instance, many governments are now demanding that polluting fish farms be located at a fai r distance from the shore.

"If you have to move your farm five kilometers away from the shore, that makes the farms much more expensive," he explained. "With this new system, we can compete."

Zohar hopes to sign the first commercial deal for his system this year. He is currently negotiating with two companies. The first venture will be located near Baltimore, so he will be available for consultation if problems arise, but in principle, he said, the system enables fish to be farmed anywhere - even in the desert.

Fish farming is a hot item these days, because demand for fish has grown as people have become increasingly aware of the health benefits of eating fish rather than meat. Partly as a consequence, however, the number of fish in the sea has been declining. Thus countries worldwide are seeking ways to meet consumer demand without decimating the natural fish population.