It started out as a graduation party concept – with lots of hot food to go with it.

Terry Castaneda’s son was a graduating high school senior and he had one wish for a party.

“My son wanted a crawfish party,’’ she said.

And a crawfish party he got. Given the enthusiasm with which the crawfish were consumed at the party, Castaneda and her daughter, Ashley Gonzalez, got the idea of cooking what Louisianans call “mud bugs’’ and selling plates out of Castaneda’s Mercedes home for friends and families. The plates went fast, and the next stop came in early 2018 when the Mercedes-made crawfish plates went up for sale at a neighborhood grocery store owned by Castaneda’s mother in Weslaco.

The plates with the mud bugs often sold out by early afternoon, and by now Castaneda knew they were on to something. It was time to give it a go as a standalone business/restaurant – and back to Mercedes they headed.

“We had no business experience,’’ Gonzalez said. “We were going to learn on the fly as we operated the business.’’

The RGV Crawfish Shack opened on 1002 W. 1^st Street in Mercedes, just off north Vermont Street. It was March 2018 and Castaneda and her daughter got busy trucking down hundreds of pounds of crawfish from Louisiana on a weekly basis. Cooking the mud bugs is a delicate and precise process. It’s best to boil and cook the freshwater crustaceans while they are alive since like all shellfish crawfish have harmful bacteria. The possibility of food poisoning is greatly reduced by cooking crawfish alive.

“We will never ever cook frozen crawfish,’’ Gonzalez said. “Everything is fresh and hand battered. We don’t let anything just sit around.’’

The Crawfish Shack was an immediate hit. Lines of customers started forming before the restaurant even opened. Heaping plates of crawfish, corn-on-the-cob, red potatoes and sausage not only looked good. They tasted great and customers from all over the Rio Grande Valley converged in Mercedes to partake of a cuisine not easily found in the region.

“If you’re not sweating, you’re not doing it right,’’ Gonzalez said of boiling and cooking crawfish. “This is not something easy to cook. It’s hard work.’’

“The shack,’’ as Castaneda and Gonzalez dub their business, expanded their menu to include catfish and shrimp baskets, po-boys, and catfish and shrimp tacos. The shack became a little slice of Cajun cooking in deep South Texas. They made their restaurant a homey place where families and friends gather. A huge chalkboard was put up along a wall where customers could write their names and couples could express their undying love for each other.

“We love it,’’ Castaneda said. “The Shack is our baby. We realize what a little jewel we have.’’

It may be a baby that will soon outgrow its modest size. The Mercedes-based mother-and-daughter entrepreneurs are now sure they’re on to something. Figuring out what that may be is something they’re still analyzing. For now, there’s plenty of crawfish to boil.

• Ricardo D. Cavazos