Infestation of Tongue-Eating Parasites Discovered in Fish Shipment

Parasites that eat fish tongues and take their place in the mouth have been found in a batch of seabream arriving at a port in the U.K.

The parasites, Cymothoa exigua, were first spotted in the packaging of the imported fish, which was picked up by the Suffolk Coastal Port Health Authority (SCPHA) when they inspected the shipment after the importer failed to complete the correct paperwork.

Upon further investigation, the parasites were found inside the mouths of the fish, in place of their tongues. The shipment, which had arrived at the Port of Felixstowe, was sent back to its country of origin, which the SCPHA did not name in its statement.

fishy parasite
The infected seabream with their tongues replaced by the parasitic tongue-eating louse, Cymothoa exigua. Suffolk Coastal Port Health Authority

Also known as the tongue-eating louse, Cymothoa exigua, as well as other related parasite species, infect a wide range of fish species worldwide, including both commercially fished species and species of no commercial value.

They enter a host fish via the gills, whereupon the female attaches to the tongue, while the male attaches to the gill arches beneath and behind the female. The female then severs the blood vessels in the fish's tongue and eats the blood supply herself, which eventually leads to the fish's tongue falling off. She then sits in the place where the tongue once was, parasitizing the fish.

"Usually, only a small proportion of the fish population is infected," parasite ecologist and expert Robert Poulin told Newsweek. "The parasite spreads when female parasites release juveniles into the water; most of these will die without ever attaching to a fish host, while a few of them will successfully contact a fish and settle in its gill cavity or mouth, where they spend the rest of their life."

This doesn't hurt the fish much, surprisingly, as there is little indication of reduced feeding or respiratory ability in infected hosts. In fact, it appears as if the fish continues to use the parasite mechanically in place of its tongue.

Danut Cazacu, a veterinary surgeon with the SCPHA, said in the statement: "Cases such as these are clear reminders of why we work hard to investigate imports and ensure they're safe for human consumption. After checking more cartons, it was apparent that most of the sea bream were infested, so we denied the consignment's entry into the UK. From there the importer can choose to have it destroyed or sent back to them, and in this case they chose the latter."

Poulin disagreed with the SCPHA's comments about the safety of the infected seabream batch.

"[The parasite's] presence certainly makes the fish unappealing and most consumers would refuse to buy and eat the fish. However, the comment in the article about 'ensuring the fish are safe for human consumption' is very misleading: the parasite is not transmissible to humans and eating it would cause no more harm than eating a crab or lobster. They are disgusting, of course, but no threat to human health."

Brenda McRory, the technical leader of the SCPHA, told the BBC that while the parasites aren't harmful to human health, the import was "not of the standards we would expect in [the U.K.]".

Stock image: Cymothoa exigua, or the tongue-eating louse. iStock / Getty Images Plus