But North Coast was also identified as the source of mislabeled fish at Not Your Average Joe’s in Westborough as part of the Globe’s 2011 investigation.

The restaurant chain said North Coast supplied southern bluefin tuna, considered a critically endangered species by an international conservation group, instead of the yellowfin promised on invoices, a contract, and on the restaurant’s menu.

North Coast officials last year denied selling bluefin tuna to Not Your Average Joe’s. But this year, Stavis conceded a bluefin may have been caught accidentally as it swam alongside yellowfin tuna and been mistakenly processed.

Industry specialists say there are ways to make the internal workings of the fish trade less mysterious for restaurant operators and consumers. Some suggest adopting a system like the one used by the European Union, the world’s biggest importer of fish. It maintains a list of approved countries that meet EU standards of seafood inspections and testing. The United States has such a system for meat, but not for the 127 countries that ship seafood here.

Others say regulators could require suppliers and restaurants to identify where fish are from. Supermarkets must label the country of origin, but restaurants are not required to.

“People want to know this,’’ said James Wright, senior editor of SeaFood Business, a trade magazine.

In addition to better oversight, industry specialists say chefs and suppliers must be vigilant to prevent one fish from being substituted for another.

For example, Union Oyster House relied on an oral agreement for its cod. Other restaurants assumed they received the correct product simply because they asked for it. Errors could be reduced if written purchase agreements listed the exact species and restaurant operators audited invoices to ensure there were no discrepancies.

“If you manage the mistakes, they should diminish to a reasonable level, and if they don’t, you’ve got a bad partner and it’s time to get a new partner,” said Dennis Lombardi, a food service industry consultant at WD Partners in Ohio.

North Coast executives said they have no obligation to make sure restaurant menus are accurate. But they conceded menu mistakes and deception ultimately hurt the company.

“We’re only as good as our customers,” Polins said. “Truth in menu is very important.”

Union Oyster House co-owner Milano said the restaurant plans to be more careful about ensuring the Boston cod dish it serves is what customers order. And even though locally-caught cod is in short supply overall, he now believes there’s enough for his restaurant.