‘Sequencing Fish Samples’ Viral Twitter Thread

On April 6 2019, a screenshots (archived here) of a Twitter thread originally published by @AwesomeBioTA one day prior went viral on social media:

In the original thread, the poster (@AwesomeBioTA) recounted the purported results of her class’s attempt to sequence samples of seafood gathered at places like supermarkets and sushi restaurants:

In at least one instance, the findings were a substitution for a better type of fish:

But other results were not as benign:

The thread concluded:

The specific claims in @AwesomeBioTA’s illustrated a larger point: seafood obtained in seemingly trustworthy ways was more often than not mislabeled. The stated results were compelling, but were they supported by evidence outside her classroom? Did that class just happen to get a bum batch of samples? The “body louse salmon” aspect appeared to compel readers the most, but so far we have been unable to find any other information about that portion of the research.

Seafood mislabeling has been a known issue in the United States since at least 2013, when a National Oceanic and Atmospheric Administration seafood inspector estimated that mislabeling occurred at a relatively small but still significant rate:

Steven Wilson of NOAA’s seafood inspection program, said he thinks the rate of species substitution “is very low,” averaging less than 5 percent.

He said purveyors are much more likely to inflate the weight of the seafood they’re selling, by adding water. Inspectors have found inaccurate weight counts 40 percent of the time, Wilson said.

Still, Wilson said that fraud was more likely to occur with certain high-value species, including red snapper and grouper. Restaurants and supermarkets frequently substituted tilapia and other cheap species in the place of red snapper, Oceana found.

A December 2018 Berkeley Wellness newsletter compiled a number of spikes in coverage in that period. That item cited conservation group Oceana as a source for the original interest in fish fraud, and an undated page on that organization’s website described an extremely broad percentage of mislabeled seafood:

Seafood fraud is the practice of misleading consumers about their seafood in order to increase profits. Along with ripping off shoppers, these actions can have negative impacts on marine conservation efforts and human health.


Recent studies have found that seafood may be mislabeled as often as 25 to 70 percent of the time for fish like red snapper, wild salmon, and Atlantic cod, disguising species that are less desirable, cheaper or more readily available.

In November 2018, the site Sustainable Fisheries took exception to Oceana’s ongoing campaign and its methods:

Seafood fraud/mislabeled seafood is a permanent topic in the sustainable fisheries space. Since 2015, news sources such as The Atlanticthe Wall Street JournalTime Magazineand the Economist have published stories on the topic of seafood fraud. Nearly every ocean conservation NGO has commented or contributed to the discourse, but Oceana has led the conversation. Oceana has an entire campaign aimed at exposing and reducing seafood fraud globally. Since 2011, they have published sixteen reports on seafood fraud—most recently, a report from Oceana Canada.

That examination noted that Oceana defined “seafood fraud” as ‘the practice of misleading consumers about their seafood in order to increase profits,’ focusing on the conservation group’s methodology:

Oceana Canada’s 2018 report exposed some important shortcomings in the Canadian seafood system and offered constructive, achievable mandates for reducing seafood fraud domestically. But the study collected data from an exaggerated sample and only presented results that supported a narrative of rampant fraudulence. The conclusions were skewed to reflect the most troubled segments of the seafood supply chain in Canada, not the entirety of the seafood industry that actually reflect national consumption trends and patterns. Recommendations to the CFIA and consumers were helpful in some cases, but unrealistic in others. My analysis to follow aims to contextualize the methods, results and conclusions of this report through the prism of foodservice and seafood industry realities.

Fundamental to the interpretation of the Oceana Canada 2018 study’s results is the understanding that the samples were selected to find fraud, not to measure the actual extent of fraud across the entire Canadian seafood supply chain. Oceana disclosed this in the report:

The investigation focused on types of fish prone to being mislabeled because of their economic value, availability or popularity. Past studies from both Canada and the United States have shown that cod, halibut, snapper, tuna, salmon and sole have the highest rates of species substitution.

In March 2019, National Geographic published an article about Oceana’s claims of seafood fraud, noting  that a full 20 percent of the 449 fish that Oceana tested were incorrectly labeled, with “sea bass replaced by giant perch,” “Alaskan halibut by Greenland turbot,” and “Florida snapper by lavender jobfish.” In that article, the outlet pointed to instances of fish fraud in Europe estimated at as high as 40 percent in previous years, but steadily improving:

Scientists in six European countries, including Dr Andrew Griffiths from the University of Exeter, tracked samples of the most commonly consumed fish, including cod, tuna, hake and plaice, after a series of studies going back 5 years had shown mislabelling in up to 40% of cases.


Of the 1,563 DNA sequence samples examined [in 2015], just 77 (4.9%) proved to be mislabelled.

Most commonly mislabelled was anchovy (15.5%), hake (11.1%) and tuna (6.8%). By contrast only 3.5% of cod and 3% of haddock was mislabelled. None of the monkfish, plaice or swordfish samples was substituted with other species.

DNA sequencing carried out in the United Kingdom and Europe did not appear to have been affiliated with Oceana, pointing to a larger existing issue in seafood mislabeling globally. Neither did a December 2018 press release from New York State’s Attorney General:

Attorney General Barbara D. Underwood released a report today titled “Fishy Business: Seafood Fraud and Mislabeling in New York State Supermarkets,” which details high levels of suspected seafood fraud and mislabeling at New York State supermarket chains. The Attorney General’s investigation, which included DNA testing, found that more than one in four samples purchased was not sold under a federally-recognized market name for that species. Mislabeling of certain popular species was rampant – including “wild” salmon (27.59% of samples sold as “wild” salmon were mislabeled), red snapper (67% were mislabeled), and lemon sole (87.5% were mislabeled). The substitutes were often cheaper, less desirable, and less environmentally sustainable species. This includes farm-raised salmon sold as wild salmon, lane snapper sold as red snapper, and swai sold as lemon sole.

A January 2017 UCLA study had similar findings unrelated to Oceana’s:

A new study from researchers at UCLA and Loyola Marymount University checked the DNA of fish ordered at 26 Los Angeles sushi restaurants from 2012 through 2015, and found that 47 percent of sushi was mislabeled. The good news is that sushi represented as tuna was almost always tuna. Salmon was mislabeled only about one in 10 times. But out of 43 orders of halibut and 32 orders of red snapper, DNA tests showed the researchers were always served a different kind of fish. A one-year sampling of high-end grocery stores found similar mislabeling rates, suggesting the bait-and-switch may occur earlier in the supply chain than the point of sale to consumers.


Over the four-year study, only bluefin tuna was always exactly as advertised. While only one of 48 tuna samples was not tuna, different kinds of tuna occasionally swapped places, including two samples that turned out to be Atlantic bluefin tuna and southern bluefin tuna, species classified as endangered and critically endangered. Out of nine orders of yellowfin tuna, seven were a different kind of tuna, usually bigeye — a vulnerable and overexploited species, the researchers said. Salmon remained a largely safe bet, with only 6 of 47 orders going awry. However, all halibut and red snapper orders failed the DNA test, and in 9 out of 10 cases, diners ordering halibut were served flounder. About 4 in 10 halibut orders were species of flounder considered overfished or near threatened.

The topic of fish fraud or seafood fraud is complex, spanning countries and continents and often appearing in the news in relation to the efforts of conservation group Oceana. An April 2019 Twitter thread about a small experiment to identify samples once again brought the issue into the social media spotlight. Some fishery experts have objected to the methods Oceana used to arrive at their broad range of percentage estimates, but independent testing carried out by the New York State AG’s office and UCLA researchers yielded similar results — the latter discovering nearly half of sushi was mislabeled. Although the scope of fish fraud or seafood fraud is in dispute, its existence is not.