DNA Testing Could Help Stave Off Fish Mislabeling For Profits

Red snapper
Red Snapper is much more expensive than tilapia, which was substituted for red snapper in many cases. Creative Commons

Let’s say you’re looking for a nice filet of red snapper at the store. You find the sign that says red snapper, go home, cook the fish, and are generally happy with what you ate. What you might not have known, however, was that the red snapper you bought was actually tilapia. Fish dealers and merchants, it seems are becoming increasingly misleading with how they label fish, which for them, increases profits, by labeling cheaper fish as more expensive species. One of the latest studies found that species in the skate family were being passed off as “sting ray wings.” Now DNA testing of these fish may be able to help slow down, or altogether prevent, something like this from happening.

DNA Barcoding and Finding Mislabeled Fish

Although DNA testing is not new, its application to fish is, and it’s proving vital to any efforts at preventing seafood fraud. To test for DNA, scientists use a slice of fish and isolate the DNA by breaking up the cells. They can either grind them, shake them in a test tube filled with tiny beads, or use enzymes to destroy the cell membrane. Afterward, they remove proteins and RNA molecules in the specimen with various chemicals. The sample is then put into a centrifuge where it spins rapidly, pulling the DNA toward the end of the tube, according to the Smithsonian.Using a system called DNA barcoding, scientists have been able to categorize the DNA of 9,769 species of fish by determining the sequence of their DNA’s base pairs and designating one specific location in the fish’s genome to recognize each individual fish.

Researchers of last week’s study used this technique and found that out of 98 wing samples from skate fish were being passed off as sting ray wings. They were all actually from six different species of skate fish, which are similar to stingrays.In February, another study found that among 120 samples labeled red snapper, there was actually 28 different species, with 17 of them not even from the snapper family, according to The New York Times. Overall, the study examined 1,215 fish, and found that almost one-third of them were mislabeled. What’s more, out of the restaurants, markets, and sushi bars that sample were taken from, sushi bars were the worst offenders. You can see a map of the mislabeled fish here

The Health Implications of Mislabeled Fish

The Boston Globe conducted its own study in 2011, and found that a number of restaurants and markets had been mislabeling fish. At Minado Japanese Seafood Buffet, for example, The Globe found that tilapia was substituted for red snapper and escolar was taking the place of white tuna. When asked, a manager said that escolar was the American name for white tuna.

Escolar, however, is a fish that cannot metabolize wax esters normally found in its diet. This causes its flesh to become oily. When ingested by humans, the oils can cause gastrointestinal problems, including severe diarrhea. The Food and Drug Administration (FDA) specifically advises against selling the fish, and even advises fish sellers to inform buyers about the dangers of eating the fish. In the February study, the tile fish, known for its high mercury content, was sold as red snapper. It was called “one of the most egregious swaps,” because pregnant women who eat tilefish can make their baby susceptible to brain and nervous system problems.

There’s not much someone can do about these issues. Oceana, the group responsible for February’s study, says that questioning sellers about their fish, especially if it’s below market value is one way to prevent eating mislabeled fish. The group also suggests buying whole fish if possible. 

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