Species substitution in fish and seafood: when fraud hides a health risk

An especially easy fraud

Seafood is one of the categories that appears again and again in food fraud reports. The reasons are well known: hundreds of species are traded, many look alike, and once the fish has been filleted, breaded or frozen, recognizing it by eye is almost impossible. Add a significant price difference between similar species and the opportunity is served up.

The FDA illustrates it with a classic example: various snapper species (Lutjanus spp.) have been sold as red snapper (Lutjanus campechanus). But the point that should worry the industry most is not the economic one.

Why the wrong species is a food safety problem

In the hazard analysis of a fishery product, many hazards depend on the species: some accumulate natural toxins, others form histamine if the cold chain breaks, others are farmed and may carry residues of veterinary drugs. The FDA's guide on fish and fishery products hazards and controls says it explicitly: species substitution can cause potential hazards to go unnoticed or be misidentified, by both the processor and the end user.

The guide itself includes a table with examples based on real substitution incidents:

• Escolar sold as sea bass: escolar is associated with gempylid fish poisoning and scombrotoxin (histamine). Labeled as sea bass, the only species hazard that would be identified would be parasites.
• Pufferfish sold as monkfish: pufferfish can contain tetrodotoxin and paralytic toxins of the PSP type. As monkfish, again, only parasites would appear.
• Spanish mackerel sold as kingfish: parasites, histamine and ciguatera are lost from view.
• Basa sold as grouper: basa, a farmed fish, is associated with environmental contaminants and aquaculture drugs, which do not appear in the grouper analysis.

The practical consequence is serious: an impeccable HACCP plan, built on the wrong species, controls hazards that do not exist and leaves uncontrolled the ones that do.

The pufferfish case in Chicago, 2007

The best-documented example occurred in 2007. Two people in Chicago prepared at home a fish that, according to the retailer, was monkfish, and developed symptoms consistent with tetrodotoxin poisoning. Both the retailer and the supplier, based in California, maintained that the product was monkfish. Genetic analysis and visual inspection determined that the fish eaten, and others from the same lot, belonged to the family Tetraodontidae, the pufferfishes.

The investigation, published in the Journal of Food Protection in 2009, led to a voluntary recall of the product distributed in three states and to the supplier's inclusion in an FDA import alert for incorrect species labeling. It is a textbook case: a substitution that looked like labeling fraud ended up as poisoning with a potentially lethal toxin.

How common is substitution?

Figures vary widely by market, species and the link in the chain analyzed. In 2015, the European Commission coordinated a control plan on white fish: 27 Member States and 2 EFTA countries took 3,906 samples of more than 150 species at different stages of the chain. The declared species was confirmed in 94% of cases, with 6% overall non-compliance that ranged from 0 to 27% depending on the country.

The Commission added an important caveat: with those data it is not possible to estimate how many cases were intentional violations for profit and how many resulted from poor practice or lack of knowledge. For the quality manager, the distinction matters little in terms of risk: the hazard to the consumer is the same whether the wrong species arrived through fraud or by mistake.

What the label requires

In the European Union, Regulation (EU) 1379/2013, on the common organisation of the markets in fishery and aquaculture products, requires informing the consumer of, among other things, the commercial designation and scientific name of the species, the production method (caught or farmed), the catch area, the fishing gear and whether the product has been defrosted. In the US, the FDA publishes The Seafood List, its guide to acceptable market names, which is the reference for labeling seafood in interstate commerce.

Requiring the scientific name in purchase specifications, and not just the commercial name, is a simple measure that closes a door: common names change between countries and sometimes group several species.

How species is verified

For fish and seafood, the reference tool is DNA. In the 2015 European plan, laboratories used protein isoelectric focusing, PCR-RFLP, DNA barcoding by sequencing and real-time PCR. The FDA identifies species by barcoding a fragment of about 655 base pairs of the COI gene, compared against its RSSL reference library.

The product's presentation conditions the method: in cooked, canned or breaded products, DNA is fragmented and full barcodes often fail, so shorter fragments are used. The details of each technique, with its advantages and limits, are in our article on analytical methods for authenticity, and the fundamentals of amplification in what PCR is.

Warning signs at purchase

The FSSC 22000 guidance on fraud mitigation lists vulnerability factors that, applied to seafood, translate into concrete signals for the purchasing and quality areas:

• A price that is too good. If an expensive species is offered far below market, the difference has to be explained by something.
• Spot purchases or new suppliers. A long, audited relationship is not the same as a one-off offer from an unknown intermediary.
• Long chains with processing. The more countries, intermediaries and process steps between catch and receipt, the more points there are at which one species can be swapped for another.
• Presentations that hide morphology. Skinless fillets, portions, breaded products, surimi or cooked products prevent any visual verification.
• Species history. Species with known substitution records, such as the red snapper mentioned by the FDA, deserve more attention.

None of these signals proves fraud, but they help decide where to concentrate analytical verifications.

Good practices for processors and buyers

• Specify each raw material by scientific name, production method and origin.
• Include species substitution in the fraud vulnerability assessment, with more weight for expensive species, species similar to cheaper ones, or those bought in processed presentations.
• Build the hazard analysis on the verified species, not only on the one declared by the supplier.
• Schedule DNA species identifications for the highest-risk suppliers and products, especially when the supplier changes or the price drifts from the market.
• Maintain lot traceability back to origin, because once fish is mixed or processed, reconstructing where it came from is much harder.

Species verification coexists with the microbiological controls specific to the category. In shellfish, for example, Vibrio spp. remains a central hazard, and both programs reinforce each other when they start from the same traceability information.