SPRING GREEN, Wis. - Let the rest of the world have its seared Ahi tuna or grilled sea bass, its sushi and sashimi. If it's Friday in Wisconsin, there's only one way to have your fish and eat it, too - fried.

The Friday fish fry is a tradition in the state where everyone seems to celebrate the end of the work week by heading to a favorite restaurant, tavern, church hall or VFW lodge for a platter of fish - most often battered and deep-fried.

"Like lemmings to the sea," Jeff Hagen jokes on a recent Friday night as he enjoys the fish fry at the Post House, a restaurant in the quiet downtown of this southwest Wisconsin community.

By day, Hagen is a tour guide at nearby Taliesen, the one-time home and studio of the famed architect Frank Lloyd Wright. But by avocation he is something of the poet laureate for the Wisconsin fish fry, having written and illustrated two books on the subject, Fry Me to the Moon and its sequel, Codfather 2.

"My cholesterol is about the same as a small town's," says Hagen, whose research for the books put 12,500 miles on his car and untold poundage on himself - damage that surely will continue as he works on his next book on hamburgers.

But this being Friday night, fish is what's for dinner here at the Post House - said to be the state's oldest continuously operated restaurant. While the full menu is available, just about everyone is ordering the fried fish.

"At least 90 percent," waitress Audrey Blau says as she shuttles between kitchen and dining room, ferrying huge platters of fried haddock.

The 31-year waitress has it herself for dinner - but before rather than after her shift, when she knows she will have lost her taste for it. "After looking at it all night," she groans.

Still, she's not complaining. Fish fry nights are generally a little easier than others, although they're also very crowded.

"Everyone usually has the same thing so you just bring one plate of fish," she says. "You don't have to make so many trips to the table."

It's a scene duplicated across the state, making Friday night in Wisconsin uniquely convivial. You might arrive with your own party at your chosen restaurant and socialize only with them, but somehow, you've connected with fellow Wisconsinites by the simple act of sitting down to the same meal.

"I don't want to sound locally chauvinistic, but more than any other place I've lived, there's more of a tendency in Wisconsin for people to come out in a communal event," says Richard March, a folklorist with the Wisconsin Arts Board who has explored his state's traditions.

"Maybe it's because of the long winters or the German gemuetlichkeit - there's more of a feeling that you're not going to sit home by yourself. And fish fries are a part of that - you tend to go to the same place, and you tend to see people you know."

Theories abound about how the Friday fish fry tradition started. Most frequently cited is the state's large Catholic population, which for years did not eat meat on Fridays. The state's lakes once provided a bountiful and cheap supply of fish such as perch - although that's no longer the case and many fish fries use frozen ocean fish.

Others say the fish fry began as a way for taverns to attract customers back after Prohibition was lifted. Among the several theories Hagen floats in his books is what he calls the "blueless in Wisconsin" factor - the state, unlike others, never had blue laws that banned minors from restaurants serving alcohol.

"You could take a whole family into a tavern," he says.

It was, and remains, a cheap night out, even for a family. Many eateries and groups such as the American Legion charge no more than $8 for a fish fry dinner, and sometimes it's all-you-can-eat.

Still, none of the theories fully explains the phenomenon. Other heavily Catholic, waterfront areas, for example, never developed a similar tradition. Nor does any of the theories explain why the fish fry has endured surviving any number of changes in how people eat (lighter, lower fat) or even practice their religion (Catholics no longer are required to skip meat on Fridays).

"It is just an integral part of life in Wisconsin," says Mike Bie, another writer who has trolled the state in search of the ultimate fish fry.

Bie's day job is as spokesman for the AAA Wisconsin auto club, but he also has recently published a guide, Classic Wisconsin Weekends, in which he includes for each of the 23 destinations tips on good fish fries in the area.

He is particularly fond of fish fries at supper clubs - another ultra-Wisconsin sort of thing. These are casual restaurants, generally out of the big city, characterized by their lazy-susan relish trays, knotty-pine walls and patrons each wearing at least one piece of Green Bay Packers attire, Bie says.

"It's important to note that a supper club is not a club, there is nothing clubby about it," he says. "Supper clubs are as egalitarian as the people of Wisconsin."

And that ultimately is what Bie enjoys about fish fries. "It's the camaraderie," he says.

Fish fries are found in a range of establishments, from plain to fancy, old to new. When a new Mexican restaurant opened recently in Marshall, a small town northeast of Madison, its owners made note that they'd be offering a Friday fish fry.

And, in fact, a Wisconsin restaurateur doesn't offer one at his or her own peril.

"I decided not to have a deep fryer in the kitchen, and I thought we'd do an alternative fresh fish," says Tom Doyle, remembering his plans eight years ago when he was renovating an old restaurant into a more upscale eatery. "People would sit down, look at the menu, see there was no fish fry and actually walk out."

After about two years of that, he decided to stop bucking tradition. Today, Doyle's Milwaukee Inn offers a more nouveau version of the common deep-fried dinners - a lightly breaded, pan-fried Canadian whitefish. On a typical Friday night, half or more of his customers will order it.

Variations on the theme are allowed, but some accompaniments are constants - coleslaw, potatoes, tartar sauce and bread, usually rye. And, for some reason, brandy variants on traditional cocktails - such as a brandy old-fashioned or a brandy Manhattan.

But the most important thing, it seems, is simply to be a part of the tradition.

"We go out every Friday night and try different places," says Ralph Kleppe, part of a foursome waiting in the bar at the Post House for a table in the dining room. "They're all good, no matter where you go."