A retired headmaster discovered a tongue-eating parasite in a portion of fish he had bought from Morrisons.
Paul Poli spotted the yellow creature as he was about to enjoy a meal of sea bass, the South Wales Evening Post reported.
The 62-year-old promptly took the fish back to the store in Trostre, where the bug was identified as a cymothoa exigua - commonly known as a tongue-eating louse.
The parasite enters a fish through the gills and then attaches itself to its tongue. It proceeds to destroy the tongue before replacing it as a new host tongue. Horrifying as it sounds, this doesn’t actually harm the fish.
Mr Poli, who said the parasite was about 3cm long and 8mm wide, has since received an apology as well as a bottle of wine and a £20 voucher from Morrisons.
A spokesperson said: “Certain fishes often pick up parasites naturally from their eco system.
“Although we make every effort to screen these out during the skinning or packaging processes , they may be present on very rare occasions.
“Our skilled fishmongers will also identify them as they fillet a fish – Mr Poli's fish was sold un-filleted at his request.”