For people ''in the swim,'' raw fish is in (or au courantm). Evidence of this latest culinary wave is the increasing popularity of Japanese sushi bars around the country. Statistics are sketchy but the trend is clear.
''Sushi is very, very, popular right now,'' says the owner of a Japanese restaurant in New York, ''but then New Yorkers always want to be chasing new trends anyway.''
In San Francisco, ''it has always been very popular,'' according to the manager of a trendy sushi bar, ''but in the past year it has picked up incredibly. . . from 5 p.m. on it's always packed.''
Even staid New England, land of the baked bean and fish cake, is taking the bait. Three sushi bars have opened here in Boston in the past six months alone.
Some 250 pounds of tuna, yellowtail, flounder, salmon, and other fish are purchased each day by one New York restaurant - and that, according to the owner , is a 30 percent increase over last year.
Two popular sushi bars between San Diego and Los Angeles are closed for expansion. Both claim they will have the biggest sushi bar in California when they reopen - each with five chefs and 40 seats.
''In the past few months,'' says one recent sushi convert in Los Angeles, ''it always comes up when a group of us get together for dinner and a movie. But usually two out of six people turn green at the idea of raw fish.''
Indeed, many Americans, having once mastered the slippery task of swallowing a raw oyster or clam, are unable to cross the divide between basic seafood and food they can see but can't identify.
The step up to the Japanese form of raw fish, however, is relatively easy, entertaining, and infinitely more dignified and elegant than slurping shellfish.
Most sushi bars are sectioned off from parent restaurants to keep out smoke and cooking smells. The traditional light varnished wood counter seats from four to 20 people although one chic Los Angeles restaurant has a counter bar of sleek black marble.
Tables may be available as well, but this denies the customer a center-stage seat for the theatrics of the sushi chef.
San Francisco boasts a restaurant with ''revolving sushi'' which travels to the customer on small wooden boats along a stream of water.
A low, refrigerated glass case, filled with neat groups of filleted fish and shellfish lying on crushed ice and parsley, runs along the top of the counter between sushi chef and customer.
The countertop and case should be spotless; a good rule of thumb is: the cleaner, the better.
In most sushi bars, a warm hand towel, presented in a bamboo basket, precedes hot soup or something to drink. Then the sushi chef places a small rectangular tray of light polished wood in front of the customer.
A mound of pink, marinated ginger, to cleanse the palate between orders, is placed on the tray along with a smaller dab of light-green wasabim, powdered horseradish mixed with water. The wasabim may be mixed in small soy-sauce dishes for added zing.
Traditionally there is no menu, and usually one is not expected to order everything at once. You can choose from fish in the glass case or from a small poster with photographs of each type of sushi with Japanese names.
Taking a stab at pronouncing the Japanese is encouraged, educational, and good for a few laughs on either side of the counter. Pointing to the desired item is a sure, but less adventurous, way to surmount the language barrier. You should also ask the sushi chef what fresh fish he suggests.
One of the most entertaining aspects of the sushi meal is watching the chef as he hand rolls and slices, exchanging banter with customers.
He is there to serve each customer personally - something to remember when tipping. Whether it is a quick snack or a prolonged dinner, he will keep making sushi until youm call it quits. (A professionally trained Japanese chef often works from five to 10 years before reaching the honored position of master chef).
There are several different types of sushi, but the most familiar is nigiri-sushi. Nigirim is the vinegared rice that the chef presses in his hand to make a small cake, then tops with a slice of fish.
A dab of wasabim, the green horseradish paste, is placed between the rice and the fish. Sashimim is the raw fish sans rice.
A good sushi chef should be able to make three or four pieces of sushi a minute - usually punctuated with a lot of palm smacking and other artistic noises. Each order consists of two pieces.
(Sushi robots, now a minor trend in Japan according to one expert, are able to make 1,200 pieces per minute).
Maki-sushim is rolled sushi - rice, fish, usually tuna, vegetables, sesame seeds, and other ingredients rolled with seaweed paper, called norim, then sliced into colorful rounds.
The emphasis in all sushi is on taste, texture, and presentation. While many of the ''flavors,'' as they are called, are strips of firm raw fish, many are made from other sea creatures. One variation is tobikom - flying-fish roe. These tiny, bright-orange jewels explode on impact. A spoonful is placed inside a hollow or ''boat'' created by surrounding the rice and horseradish with a thin wall of norim.
The chef then artfully slices thin cucumber wedges about the size of a quarter and spreads them into a fan shape. This serves as a backrest for a bright-yellow quail egg yolk.
The chef peels back a strip of eggshell with a heavy knife, separates the egg , and drops the yolk on the waiting roe boat.
It is all supposed to go down in one bite. Yolk, tobikom, cucumber, crackly nori, wasabim, and rice.
Not all sushi is raw. Cooked shrimp, crab, and lobster, as well as smoked salmon and marinated mackerel, are good items for the sushi beginner to try.
One can also ask for special hot sushi. Many times a small toaster oven behind the sushi bar is used to turn salmon skins into crispy baconlike strips.
Broiled yellowtail in a sweet sauce is another specialty. One of the strangest-sounding but most delicious treats is warmed sea eel, called anagom, combined with cucumber strips, sesame seeds, and a sweet brown sauce. The ingredients are then wrapped with norim into a cone-shape roll that one tackles like a taco - head on.
Before venturing into a sushi restaurant, it is a good idea to learn some sushi etiquette to avoid embarrassing yourself with soy-sauce-soaked rice balls disintegrating in your fingers and fish falling all over the place.
Use your fingers for sushi. Chopsticks are for small side dishes offered by the chef ''on the house'' to special customers, or on a whim if he has something especially good.
If tasting some of your dinner partner's food, use the opposite end of your chopsticks.
One of the most important things to remember is to dip the fish and not the rice into the soy sauce. The prepared rice has its own special flavor, which the soy sauce destroys. When possible, the sushi should be eaten in one delicate bite.
Never ask the sushi chef for the bill. The waitress is your go-between for everything except the actual fish orders. She brings the hot towel to begin with and the check at the end - which, the reader must be warned, may sometimes be more sobering than the initial idea of facing raw fish.