I ADMIT when I first heard about Gumbo Jumbo, a Cajun-Vietnamese fusion restaurant in downtown San Jose, I dismissed it as one of the most improbable restaurant concepts I'd ever heard of, right up there with Icelandic-Mexican food or vegan barbecue.

But a few weeks ago, I was on a restaurant scouting mission on Story Road, ground zero for the Little Saigon/ Saigon Business District brouhaha. I just call it "that part of south San Jose where all the great Vietnamese restaurants are." As I scanned the strip malls for new and interesting restaurants, I spotted Crawdaddy, a Vietnamese-American-owned restaurant that specializes in boiled crawfish and all things Cajun. That's interesting, I thought, as I drove on. Further down the road I saw the generically named Crawfish Seafood Restaurant, another Vietnamese-American-owned business that touts its boiled crawfish and fresh seafood.

I'm sometimes slow to catch on to the obvious, but it dawned on me that maybe there was something going on with all these Vietnamese crawdad restaurants that I didn't understand.

Further investigation revealed the existence of at least four others, with another one in the works. It was a culinary riddle: What were Vietnamese-American restaurateurs doing serving a Deep South specialty made popular by French Canadians exiles who settled in Louisiana's bayou country? Culinary and cultural anthropological questions started to swirl in my head. Guided by a powerful hankering for some boiled mudbugs, I decided to investigate.

While all the restaurants I visited specialize in boiled live crawfish, none are quite alike. Some offer a menu of Cajun and Southern fried classics like boiled shrimp, fried catfish, po' boy sandwiches and fried oysters. Others, like Gumbo Jumbo, have charted new territory with their Cajun Vietnamese fusion dishes such as the delicious Cajun lemon-grass chicken, garlic shrimp noodles and crawfish eggrolls. Still others offer a typical Vietnamese menu of rice and noodle dishes alongside steaming bags of crawfish. I even saw one old-line Vietnamese restaurant that had recently hung out a banner advertising they were now serving crawfish, obviously hoping to cash in on the crawdad craze.

At all the restaurants I visited, crawfish is sold by the pound. Ten bucks a pound is about the market rate. The little red buggers are boiled in an aromatic broth and then ladled with different combinations of butter, garlic and cayenne pepper, quite different from the more simply prepared crawdads I've had in New Orleans. The crawfish arrive in a transparent plastic bag and are plopped on the table. They swim in a buttery broth that's generally available from mild to fiendishly hot. Most places will toss in some pork sausage and an ear of corn for a buck or two more. The sausage can be good, but the corn is usually quite gummy.

In addition to the extreme spiciness, the only other Vietnamese touches are the lime wedges that come with little plastic ramekins of salt and pepper. What you do is ladle a little of broth into an empty ramekin, squeeze in some lime juice and sprinkle in a bit of salt and pepper. Then you dunk your crawfish into the doctored-up sauce. The lime juice helps cut the richness of all that butter and really brings it to life. It's a great combination.

Eating crawfish is a messy, visceral experience. If you've never had them before, you do it like this: twist and pull the tail from the body. Pinch the tip of the tail and with the other hand crack the first few segments of the shell and tug the meat free. Eat it, but don't stop there. Pick up the head and put the cavity to your mouth and suck deeply to free the little fatty liver within. Repeat as often as necessary with a cold beer close at hand.

It's the sauce and the freshness of the crawfish that distinguish one restaurant from another. Of the four places I visited, my favorite was Crawdaddy, a spare, clean restaurant with butcher-paper-covered tables and flat-screen TVs on the walls, owned by first-time restaurateur Thai Nguyen. He flies in boxes of live crawfish from Louisiana. When it's not available he gets product from the Sacramento Delta. The specimens I had were sweet and springy fleshed and the garlic and cayenne–spiked butter sauce was so good I almost took home the leftover dregs at the bottom of the bag.

Nguyen went to Milpitas High School, but his family is originally from Houston. After he got laid off from his high-tech job, he looked around at the growing number of crawfish restaurants and decided to open one himself 10 months ago. He doesn't know why so many Vietnamese are getting into the crawfish business, but he wanted a piece of the action.

"I just saw it as a gold mine," he says. "I see it as the next sushi. It's adventurous food. You put on a bib and get down and dirty."

Gumbo Jumbo is quite good, too. With its exposed brick walls, high gloss wood floors, white tablecloth–covered tables and lounge, Gumbo Jumbo is the most upmarket place I visited.

Co-owner Amanda Nguyen (no relation to Thai Nguyen) moved from Ft. Worth, Texas, to open the restaurant with friend Quyhn Nguyen. Amanda Nguyen owned an Asian fusion restaurant in Ft. Worth and saw the potential for a Cajun-Vietnamese restaurant in San Jose, given its large Vietnamese population and the popularity of Viet Cajun restaurants in Texas. They opened a year ago.

While she promotes her crawfish, Amanda Nguyen said she developed a diverse menu in order to appeal to a wide clientele.

"I don't want to just cater to the Vietnamese," she said.

While the profusion of these restaurants is new to Silicon Valley (most opened within the last year or so), the Viet Cajun concept is not a new one. These restaurants started out on the Gulf Coast and particularly in Houston, a city with a substantial Vietnamese population where many work in the shrimp and seafood processing industry. From the Gulf, the restaurants migrated to Orange Country, home to the largest Vietnamese population outside of Vietnam.

Robb Walsh, restaurant critic for the Houston Press, wrote a story on so-called "Asian Cajuns" in 2002 as part of series on fusion food in Houston. Vietnamese and Cajun food are similar, he says. Rice is the basic staple of Vietnamese and Louisiana cookery and both rely on fresh seafood and chile peppers.

"Since both were also once French colonies, they speak the same language in the kitchen; baguettes, beignets and café au lait are as well known in Saigon as in New Orleans," he writes. "Poor boys and bahn [sic] mi thit are remarkably similar, despite the fact that they evolved half a world away from each other."

Louisiana rice fields aren't so different from Vietnamese rice patties. In Louisiana, crawfish are grown in rotation with rice. Rice fields are flooded with water and then stocked with crawfish. In Vietnam, rice paddies host a number of edible mollusks and crustaceans that form an important part of people's diets.

Walsh describes Viet Cajun as an example of syncretism, a word anthropologists use to describe the absorption of one culture's traditions by another.

Andrea Nguyen, a Santa Cruz–based food writer and Vietnamese food expert, hasn't sampled San Jose's Viet Cajun restaurants, but remembers how her late uncle would whip up impromptu crawfish feasts when she lived in Southern California.

"In the spring, after the rains, he and his sons would go to some undisclosed river and bring in what seemed like a ton of crayfish," she wrote in an email. "They'd boil them up and bring them in plastic grocery bags to our house in Orange County. We'd sit around the dining table and twist the heads off, crack the tail shell and pop out the flesh. A little dip in salt, pepper and lime juice was all they needed. It was a multihour midday meal. Fabulous."

She calls the wave of Viet Cajun crawfish joints "nhau restaurants" (pronounced "n-yow"), a great Vietnamese word that means to drink beer, snack and have a good time.

"It's the kind of food that speaks to Viet people. Little crustaceans you can pick at, nibble on, while talking to friends," she says. "It's a social thing—trendy Viet dining. It's nhau food for noshing, celebrating, having a fun party scene with friends and family."

The crawfish boil may have been born on a bayou, but seafood and beer-loving Vietnamese are helping spread Viet Cajun far and wide. It's a competitive market here in Silicon Valley, and some of the new restaurants likely won't survive, but in the meantime let's nhau, y'all!