CHICAGO – Diners who think they are eating red snapper may actually be munching on gold-banded jobfish.

Those who order Alaskan cod may really be tucking into a threadfin slickhead. And fans of yellowtail could just be getting a fish tale.

These are some of the findings of a fish fraud investigation released last week by the ocean conservancy group Oceana.

After its troubling seafood fraud investigations in cities on the East and West Coasts over the last two years, the group expanded its testing to other cities.

The group does not list the names of the restaurants or stores where it bought the fish because “we didn’t know where, along the supply chain, the mislabeling first occurred,” said Beth Lowell, Oceana’s seafood fraud campaign director. “So we didn’t want to call out businesses that may not have known their fish was mislabeled.”

Improperly labeled fish can cost consumers financially, but these substitutions also can have health consequences. In many cities, purveyors were found to be marketing white tuna that was actually escolar, which is cheaper and can cause severe digestive problems.

Among the places where testers bought the samples, sushi bars fared the worst, with 14 out of 22, or 64 percent, of the samples coming back as erroneously labeled. In contrast, 20 percent of fish sold at other types of restaurants and 24 percent of the seafood sold at grocery stores was mislabeled. Oceana said that it focused mainly on large grocery chains.

Lowell says consumers can minimize their risk by patronizing businesses that make an effort to source sustainable fish, are willing to answer lots of questions about the product, and can show you the whole fish even if you are only going to buy a fillet.

Dirk Fucik, owner of Dirk’s Fish & Gourmet Shop in Chicago’s Lincoln Park section, says he does all that but is not surprised that others don’t.

“It’s unfortunate, but this has been going on in the seafood business for a long time,” Fucik said. “The U.S. imports about 25 million pounds of a Vietnamese catfish called basa [or pangasius] every year. When’s the last time you saw that on a menu?”

Americans may be particularly vulnerable to fish fraud because of their preference for white-fleshed fish with little taste variation.

“Most other countries show a preference for oilier, more flavorful fish, but Americans like their fish on the milder side,” said Christopher Martinez, a manager at Dirk’s. “And with a lot of those mild varieties, if you remove the fillet from the fish and take off the skin, you can call it just about anything.”

Gavin Gibbons, spokesman for the National Fisheries Institute, a trade group, says he’s always glad to see “people shining a light on fish fraud.”

But, he said, reports such as Oceana’s “can negatively impact the whole community, and disproportionately those who are not engaging” in fraud.

It would be more helpful to go deeper, he said, and find where the fraud originates: at the dock, the distributor, the retailer or some point in between. “We feel like these investigations leave the loop unclosed,” he said.

A 2011 investigative series by the Boston Globe reported that at least some of the fraud started at the distribution level. It said suppliers had been labeling escolar, for example, interchangeably with white/albacore tuna. The Globe noted that the less expensive escolar is not even in the tuna family.

Until better enforcement or traceability becomes a reality, Lowell advises consumers to seek out retailers that welcome detailed questions about their fish. Gibbons says consumers should ask retailers whether they buy from distributors who are members of the Better Seafood Bureau, a voluntary group that pledges to abide by ethical guidelines and accept audits if they receive a certain number of unresolved complaints.

Finally, all warn that if you find certain seafood items at a price that sounds too good to be true, it probably is.