Cod and brill fillets sit on display. (Simon Dawson/Bloomberg)

In the bizarro world of seafood fraud, a fish is not always what it seems.

When sold in Brazil, largetooth sawfish — a species classified as critically endangered — becomes anonymous “shark.”

When sold in a certain Santa Monica, Calif., sushi shop, illegal whale meat became fatty tuna. (The restaurant has since shut down.)

And when sold across the United States, cheap Asian catfish becomes one of 18 types of white fish fraudsters want it to be, according to a recent report.

Worldwide, one in five pieces of fish meat is incorrectly named on the menu or label, revealed the new survey representing 25,000 fish samples.

Oceana, a marine conservation and advocacy group, released the report on Wednesday, and updated the global map it created in 2014. The new map is interactive and highlights news stories of restaurant fraud, as well as DNA analysis and other scientific studies.

The organization culled the data from Google Scholar, news alerts and legal cases for seafood mislabeling. The end result is somewhat akin to a medical literature review, including 200 published studies from 55 countries and every continent except Antarctica, focused on the seafood industry.

“The path seafood travels from the fishing boat or farm to our dinner plates is long, complex and non-transparent, rife with opportunities for fraud and mislabeling,” said Oceana director Beth Lowell in a news release. In its review, Oceana found signs of fraud in every part of the seafood process — mislabeling occurred when the fish were caught, processed, shipped, distributed and sold.

The report marks one of the most comprehensive warnings in a long line of concerns about the fish industry. The issue has found support all the way to the highest levels of government — President Obama established a task force in 2014 to cut down on fish fraud in the United States.

“Our nation’s fisheries remain threatened by illegal, unreported, and unregulated fishing and seafood fraud, which negatively affects our markets,” Commerce Secretary Bruce Andrews said in March 2015. As The Washington Post reported last year, the task force’s ultimate goal is to track all the fish and crustaceans that enter U.S. ports.

The United States fares worse than the global average, according to the Oceana report. Fraud was present in 28 percent of fish sold, according to the averaged rate extrapolated from U.S. studies conducted between 2014 and 2016. (The global normalized average is 19 percent.)

Asian catfish — also known as pangasius, basa or river cobbler — was a prime offender. With powers of transmogrification like a walleyed and flaky Jaqen H’ghar, the “Game of Thrones” face-changer, the catfish’s mild, white meat has been passed off as cod, perch, grouper and 15 other fishes.

The fish, raised in Vietnam, may be up to $1 per pound cheaper than American catfish, the Associated Press reported in 2006. U.S. catfish farmers have been pushing back against the legal import of pangasius, claiming unsanitary farming practices in Southeast Asia. Catching the Asian catfish as it slips across the border as faux grouper, however, may be a tougher target.

There are several health concerns about mislabeled fish, depending upon the pretender species. Escolar, the third-most common substitute fish worldwide, has been called the “Ex-Lax fish” because it contains gempylotoxin — an oil that can cause anal leakage.

Oceana also warned about fish related to tuna, like mackerel, that when spoiled may trigger histamine food poisonings similar to allergic reactions.

Lowell called for improved tracking methods of fish.

There is successful precedent. In the European Union, the Oceana report indicated that fraud rates fell from 23 percent in 2011 to just 8 percent in 2015.

The group’s analysis is still preliminary, it said, but it suggests that heightened public attention, increased fraud investigations over the past dozen years and better catch documentation lowered rates of mislabeled fish in the E.U.

“Without tracking all seafood throughout the entire supply chain, consumers will continue to be cheated, hard-working, honest fishermen will be undercut,” Lowell said, “and the long-term productivity of our oceans will continue to be in jeopardy.” Until then, you’ll have to believe that it’s not snapper, at least one time out of five.