What’s Really in Your Sushi?

28 Apr 2014
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Escolar is an oily, deepwater fish that can grow to over 3m in length. This species cannot metabolize the wax esters found naturally in its diet, and, as a result, is sometimes referred to as the ‘Ex-Lax Fish’, because human consumption of escolar is notorious for causing gastrointestinal problems.

Escolar’s wax ester content can cause gempylotoxism or keriorrhea (greek for ‘flow of wax’). Keriorrhea occurs when the body expels yellowish-orange drops of oil instead of bowel movements. Other symptoms of keriorrhea, which may occur between 30 minutes and 36 hours following consumption, include stomach cramps, diarrhea, headaches, nausea, vomiting, and anal leakage.

So now we are aware of this delightful list of possible adverse effects, we know not to eat escolar. But what if you don’t know that you are eating it?

Escolar is significantly cheaper than tuna, and as a result it is often substituted for tuna, and mislabeled as ‘white tuna’ by fish markets and restaurants. Escolar might also be mislabeled as butterfish.

In 2009, tuna samples from sushi restaurants in New York and Denver were DNA tested to determine their contents. The study looked at the use of DNA barcodes to identify fish sold on the market. One of the findings of the study was that 19 restaurants were unable to clarify, or misrepresented, what species they sold. The researchers also found that five of the nine samples sold as a variant of ‘white tuna’ were not albacore, but escolar (1).

The sale of escolar has been banned in Italy and Japan due to its ability to cause gastrointestinal problems. The FDA has not banned the sale of escolar, but advises “against the sale of the fish in intrastate/interstate commerce, and requests that seafood manufacturers/processors should inform potential buyers/sellers, etc. of the purgative effect associated with the consumption of these fish” (2).

In 2013, the conservation group Oceana released a report detailing the results of a large study it had undertaken. Oceana collected 674 food outlets, in 21 US states, and DNA tested them. The study found that 33% of the 1,215 samples collected were mislabeled (3). Ashley Blacow, Pacific Policy and Communications Manager for Oceana, stated that one of the most common switches seen involved white tuna, or albacore.

Some states are starting to take this seafood fraud seriously; new legislation is currently passing through the senate in California that, if successful, would make it illegal for anyone to knowingly sell mislabeled seafood in this US state.

Unfortunately, mislabeled seafood fraud is widespread, and little is being done currently to stop it. Until this type of fraud is taken more seriously by the authorities, it might be wise to steer clear of white tuna, unless you want to risk some very unfortunate side effects.

Watch this video to see Professor Chris Elliott, Director of Institute for Global Food Security at Queens University, Belfast, discussing fish fraud. Find out more about how researchers are using advanced mass spectrometry techniques to investigate fish fraud, and also to determine fish sustainability.

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Sonia Nicholas
Clinical Diagnostics Editor