DNA tests find shark sold as corvina in Ecuador

Nearly half the fish sold as “corvina” in sampled Ecuadorian markets turned out to be shark meat, according to a study published in Frontiers in Marine Science and reported by El País. Researchers tested fillets bought in markets in Quito, Cuenca, Ibarra, Ambato, Manta and Guayaquil, then used PCR-based methods at the San Francisco de Quito University (USFQ) to identify species from small tissue fragments.

The results point to a trust problem that regulation has not priced correctly. The team found that about 47% of “corvina” samples were actually shark, with positives concentrated in Andean cities where fish consumption is less common and buyers are less able to identify species by appearance. In coastal markets, customers and vendors have more practical knowledge; inland, the product is already abstracted into uniform fillets. That is where relabeling pays.

The study’s method is straightforward: one PCR test screens for shark; a second identifies the species, with a reported 97.8% effectiveness in that step. Among the species detected were silky shark and smooth hammerhead—both listed as vulnerable by the IUCN—as well as pelagic thresher and blue shark. The smooth hammerhead is fully protected in Ecuador, meaning it cannot be legally caught even as “bycatch,” and cannot be sold.

Ecuador’s rules allow the sale of sharks caught “incidentally,” a category that, in practice, can absorb industrial-scale volumes. The authors warn that this provision could facilitate the sale of more than two million sharks per year, while creating cover for protected species to enter the supply chain. Once the fish is filleted and relabeled, enforcement becomes a paperwork exercise: inspectors need either chain-of-custody documentation that can be forged or laboratory capacity that is rarely stationed at market stalls.

That is why the paper’s most practical implication is institutional rather than biological. PCR is described as low-cost and accessible—familiar to the public after Covid-19—and can be deployed beyond academia. El País quotes researchers arguing that the public sector should incorporate these tools so that verification is not left to sporadic studies and consumer suspicion. Without routine testing, the market rewards the cheapest substitute that can pass as a premium fish.

In Ecuador’s inland markets, the study suggests, “corvina” has become a label that can be printed on almost anything—until a lab looks at the DNA.