The physician, a visiting surgeon from Japan, worked swiltly. He had scheduled four patients for life-or-death cancer surgery, and he faced an ususnal hardship: If he failed to complete each operation within 20 minutes, the patient would die.

The patients were not humans. They were fish that could survive out of water and on the makeshift operating table for only a brief period.

That a surgeon, and not a veterinarian, was called in to perform these operations suggests that these were not ordinary fish -- and they were not. The four cancer patients, three of which survived, were koi.

To the uninitiated, koi (pronounced "coy") appear a bit like overgrown goldfish. But the major resemblance between koi and the typical dime-store goldfish is that they both swim. Koi, pound-for-pound one of the most valuable creatures in the world, have been known to sell for more than $100,000 each.

Their value is as a feast for the eye, not the stomach. A species of carp, they were introduced into the Orient in the 13th century by Genghis Khan, who discovered the fish during his conquest of Persia. Fascination with the spectacular coloring and patterning of the creatures later spread to Japan. There, they were dubbed koi, which means "living jewels."

For centuries, the breeding, raising and exhibiting of koi was an art confined almost entirely to the Far East. But in the past 20 years it has spread steadily, into the United States, South America, Britain and South Africa.

Hawaii, with its large Oriental population, was the first U.S. state to import koi in large numbers from Japan, the heartland of the koi culture. California, which also has a large Japanese community, is the second leading state in koi population. And the movement has begun to take hold in some Sun Belt states and in a few locations on the East Coast.

In fact, although the art is still in a relatively rudimentary stage in the United States, it has advanced to a point where a growing number of Japanese koi fanciers annually visit American shows, and some U.S.-bred koi have been exported to Japan.

The center of koi activity in California is the tiny San Diego County community of Fallbrook. Nestled in the rolling hills on the edge of town, amid avocado and citrus groves, was a former chicken ranch that is now California Koi Farms, Inc., the largest company in the United States exclusively devoted to breeding and raising koi.

The operation was started in 1974 by Yoshihiko Adachi, owner of the Adachi Fish Farm in Yonago, Japan. Adachi commutes regularly between the two farms. His son, Takemi, supervises breeding and other daily operations at the Fallbrook facility. Ralph Pickering, the general manager, handles the farm's business affairs.

"There's not a fish in there that isn't worth $1,000 or more," Pickering said recently, pointing to a pond full of year-old koi. On its 10 acres, the Fallbrook farm has 100-foot-square clay-lined ponds for raising the koi, a half-dozen concrete-lined breeding tanks, two ponds for segregating breeding-quality males and females and a "Sun City" pond for over-the-hill fish.

Over the centurles, selective breeding has produced 13 distinct varieties of koi (it takes about 100 years to develop a new strain of the fish.) Variations in pattern and scales are almost infinite in modern koi, and their electric colors range from brilliant reds, golds, platinum to blues and black. Some of the variegated koi have a metallic sheen.

The average lifespan of pond-raised koi is 20 years, but some live a century or more. Koi U.S.A., a magazine for koi breeders, recently ran an obituary on a red carp that died last year at the age of 214.

Koi can grow up to 42 inches in length. But factors other than age, such as the size of the pond they live in, determine growth. The 214-year-old, for example, was less than 29 inches long when it died.

Above the raising ponds at the Fallbrook farm are rows of wire strung from one end to the other, to discourage hungry hawks. But herons, not hawks, are the big threat, because they can slip beneath or through the wire. Killing the birds is forbidden. They are protected by federal wildlife regulations.

"When the herons come, we do a lot of running around, yelling and arm-waving," Takeni Adachi said.

Various diseases and parasites also take their toll. Medication is usually added to the water or, in some cases, by individual hypodermic shots.

Considering the high value of some of the koi, security would seem to be a problem -- but it isn't.

"No one would steal a champion-quality koi," Pickering said, "because the only point in owning one is to show it, and it would be spotted immediately." So far, no one has tried to kidnap one of the farm's $20,000 or $30,000 fish for ransom, and besides, Pickering said, "We keep the really good ones at home."

Just keeping the farm's 1 million-plus fish alive is a seven-day-a-week job. Each day the general manager makes his rounds, checking water temperature and purity and handing out about 80 pound of fish food imported from Japan.

At feeding time, he stomps several times on the bank of each pond. The fish quickly learn that the motion signals chow time, and they swarm toward him for a handout.

In the office, Takemi Adachi has a thick record book with a photograph and pedigree of each breeder koi. Breeding records have been kept for centuries in Japan but their accuracy was sometimes questionable. "In the old days, before cameras, they kept a drawing of each fish. Sometimes the drawings weren't very good, and one breeder got mixed up with another," Adachi said.

As the fall breeding season approaches, he takes down the record book and begins selecting which males will be bred with which females. The process, difficult to perform and impossible to describe, requires Adachi to envision the characteristics that might emerge when particular fish are bred.

One female and two maies are selected and placed in a tank strung with artificial grass. After breeding and after the eggs are laid in the grass, the adults are immediately returned to their respective ponds to prevent them from eating the eggs. A female lays about 300,000 eggs at each breeding. In three days, about 250,000 babies hatch and they are removed to a special pond.

"That's the time of the year we hate," Pickering said. "The baby fish require a special diet of hardboiled eggs ground up with flour and water. It takes about 40 to 60 eggs a day to feed them. We boil them in the house and you know how they stink up a place. None of us can look at an egg for about three months."

Nature thins the babies' ranks considerably, and then Adachi and Pickering take over. Koi come in three grades: those with potential to become show champions, those good enough to show but that have little chance of winning and decorative fish -- the ones that end up in restaurant and hotel ponds. The latter group are considered "junk fish."

When the babies are six weeks old, Adachi and Pickering cull 60 percent to 70 percent of them. The culls (poor quality koi) later are sold to wholesalers for a few cents each. Another 10 percent are culled six weeks later. The remaining fingerlings are considered exhibition or champion quality. Then they mature, the exhibition-grade fish sell for several hundred dollars each.

Champion-quality koi sell for $1,000 and up, depending on their size. "We sell about 150,000 fish a year," Pickering said, "and if we raise 10 champions, we've had a good year.

Champions are chosen at snows, five of which are held each year in California. The shows are scheduled during the cooler months when it is safer to transport the koi, which are vulnerable to heat. Exhibitors come from several states, including Hawaii, and from as far as Japan and South America. All the judges are flown in from Japan.

The biggest exhibition of the year, the First U.S.A. International Inshikigoi Show, was held near Los Angeles in Gardena Civic Center in February. Four experts brought in from Japan for the occasion judged the 1,000-plus entries. In the average show, by comparison, 500 to 600 fish compete. The shows are held outdoors.

Tanks are set up in rows,with the fish segregated by breed and size. Specators are free to roam the exhibition area before the competition begins, but judging koi requires such intense concentration that the public is cleared out of the immediate area during that period. Owners are allowed to remain but if they speak the judge will break off and glare until they stop or leave.