Chicago diners who think they are eating red snapper may actually be munching on goldbanded 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 Chicago fish fraud investigation to be released Thursday by conservancy group Oceana.

After its troubling seafood fraud investigations in East and West Coast cities over the last two years, the group expanded its testing to other cities, including Chicago. Thirty of 93 fish samples taken from Chicago restaurants, retail chains and sushi bars were mislabeled, mirroring percentages found in other cities.

Eight of nine Chicago red snapper samples tested by Oceana turned out to be different fish, the report said. And none of the three yellowtail samples tested was actually yellowtail. Single samples sold as corvina, jack, mackerel and even perch did not match those descriptions, according to Oceana's DNA tests.

The ocean conservancy organization 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. As in many cities, Chicago purveyors were found marketing white tuna that was actually escolar, which is cheaper and can cause severe digestive problems.

On a reassuring note for local fish fans, every one of the 22 salmon samples Oceana tested in the area checked out just fine. Ditto for the seven halibut and seven grouper samples — a surprise, Oceana noted, because grouper has frequently been found mislabeled elsewhere.

Among the places where testers bought the samples, sushi bars fared the worst, with 64 percent (or 14 out of 22) 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 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 and Gourmet Shop in Lincoln Park, says he does all that, but he's not surprised that others don't.

"It's unfortunate, but this has been going on in the seafood business for a long time," said Fucik, a veteran fishmonger and a former co-owner of Burhop's. "The U.S. imports about 25 million pounds of a Vietnamese catfish called basa (also called 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, he thinks reports like 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.

The Food, Drug and Cosmetic Act is enforced by the U.S. Food and Drug Administration and prohibits the mislabeling of food. In October, after another Oceana report, Sen. Barbara Boxer, D-Calif., and scores of seafood advocates sent letters to the FDA urging it to combat fraud with stepped-up inspections.

Boxer noted in her letter that fraud isn't just "deceptive marketing, but it can also pose serious health concerns, particularly for pregnant women seeking to limit exposure to heavy metals or individuals with serious allergies to certain types of fish."

In 2007, for instance, two Chicago diners became seriously ill after being served puffer fish that was sold as monkfish.

Industry watchers suspect the main motive for fish fraud is profit, but Gibbons says it can be used to hide the country of origin and thus certain duties and tariffs. Lowell says it can also be used to sell overfished varieties to those trying to avoid them or to swap cheap imported farmed fish for wild caught varieties.

"Red snapper in sushi restaurants was often tilapia," Lowell said. "The customer might be thinking this is wild caught fish from the Gulf of Mexico, but tilapia is often farmed in parts of Asia that do not adhere to the same standards as we have for aquaculture here."

According to Oceana, more than 90 percent of American seafood is imported and yet the Government Accountability Office in 2009 reported that only 2 percent of imported seafood is inspected by the FDA and less than 1 percent is inspected for mislabeling.

Last week the FDA responded to Boxer's letter, saying it has recently invested in DNA-testing equipment and has encouraged state and local authorities to do the same. In 2012 FDA gathered approximately 800 fish samples for testing and "once we finish compiling results, FDA will have a better idea of where to conduct future sampling and enforcement efforts," the FDA letter said.

The FDA letter said the new Food Safety and Modernization Act restricts its data access only to the "immediate previous source and immediate subsequent recipient of food."

The National Fisheries Institute argues that existing laws, if enforced by the FDA, can solve the fish-fraud problem. It disagrees with advocates and others who seek additional regulatory power for the FDA.