This is the most repulsive fish I've ever seen," pronounces Alan Davidson, which is a strong statement, since he is the world's leading authority on seafood. Yet that doesn't stop Davidson, a former British diplomat, from proceeding to gut the creature, a bony-backed catfish, sent for his delectation from Brazil. His eyebrows do arch as the orange innards spill out, but soon a mess of fillets is sizzling in the frying pan. "Not a sharp taste," he adjudges after the first bite, "but a distinguished taste."

Already author of definitive works on the seafare of the Mediterranean and of Southeast Asia, Davidson, 56, has just published North Atlantic Seafood (Viking, $15.95), in which he catalogues some 220 indigenous edible species. He also includes more than 270 international recipes native to the bordering shores, from Russian borscht with squid to Maryland stuffed shad roe. The compendium is richly flavored with 19th-century line drawings, historical anecdotes, wit and pungent opinion.

"Americans are spoiled," charges Davidson, as peppery in person as in print. "With such an abundance of fish around them, they've eaten only the best. But fish stocks are dwindling, and people must realize some of the less attractive varieties are quite tasty." His current book devotes four pages to "Miscellaneous Uncouth Fish," including the goosefish, which yields in its tail a white, firm meat that Davidson claims can pass for lobster. "I like to be one step ahead of the public," he notes. "Julia Child is eating some goosefish now, and the price has gone up."

Born in the seaport of Londonderry in Northern Ireland, Alan was a tax inspector's son who attended Oxford on scholarship and earned top honors in classics and philosophy. He served in the Royal Navy during World War II before traveling the globe for 27 years in the diplomatic corps. In 1950, while stationed in Washington, he met his American-born wife, Jane Macatee. In 1962, while assigned to Tunis, they were baffled by the array of unfamiliar fish in the local market, and when no reference book was to be found, Davidson compiled his own. Mediterranean Seafood became a classic, followed after he was ambassador in Vientiane by Fish and Fish Dishes of Laos and Seafood of Southeast Asia.

By 1975 he was intrigued enough with the subject to take early retirement, and now the Davidsons of London are as prolific as the Wallaces of L.A. Husband and wife translated Alexandre Dumas père for Dumas on Food, and their three daughters all have their oars in. For North Atlantic Seafood, Pamela, 25, wife of a Soviet scientist in Moscow, contributed the Russian recipes. Caroline, 27, married to a British journalist in Washington, is readying the introduction to a reprint of a 1736 English cookbook. That will be published by Prospect Books, a Davidson-controlled house in which Jennifer, 21, a Cambridge graduate, helps with editing. Prospect also puts out Davidson's new quarterly, Petits Propos Culinaires (Culinary Small Talk).

The patriarch, often attired in a mandarin-style jacket and Buddhist medallion, both souvenirs of his favorite posting, Laos, works out of a four-story Victorian house in Chelsea. His projects include Science in the Kitchen, inspired by seminars he gave last year at his alma mater, and the Oxford Companion to Food, a proposed 1,000-page reference book. For his seafood series, he plans next to plumb the Caribbean and the Gulf of Mexico. He's also written a political thriller about a NATO kidnapping, Something Quite Big, and ignored a British Foreign Office request not to publish it.

Davidson fished as a boy, but the sport now makes him impatient: "I'd much rather repair to my library and get on with my reading." He does enjoy cooking, but farms out the majority of his recipes for testing.

"I believe in a variety of approaches," he says. "If a fish is truly fresh, with a good flavor of its own, it's fine over charcoal. Or eat it raw, as the Japanese do." Yet for all his research and years abroad with the navy and foreign service, Davidson's favorite fish, confides his wife, are mainstays he grew up with: cod cooked in milk or kippers.