Polish seaside restaurants serve butterfish linked to severe oily diarrhea

In Poland, coastal fry‑shops commonly offer “butterfish,” a trade name for either the deep‑sea species eskolara (Lepidocybium flavobrunneum) or kostropak (Ruvettus pretiosus). Unlike Italy and Japan, where the fish is banned, it is sold legally in Poland as a cheap alternative to cod or flounder.

These fish contain high levels of wax esters, known as gempylotoxin, which the human digestive system cannot break down. The compounds pass unchanged through the intestines, causing an orange, oily diarrhoea called keriorrhea, along with abdominal cramps, nausea, dehydration, headaches, and skin reactions. Symptoms typically appear two to three hours after consumption. Medical studies from 1981, 2009 and 2018 have documented these effects.

Consumers are advised to avoid vague menu items labeled simply “butterfish,” inquire about the exact species, and consider more familiar fish such as Baltic cod, especially when the price seems unusually low.