This paper presents data on a phenomenon accidentally observed during a long-term study,
which was originally carried out to examine seasonal changes in the activity of European catfish.
We found a conspicuous increase in the movement and relocation of European catfish
in winter and tested our hypothesis that these behavioural changes were induced by oxygen
deficiency. We further discuss the inefficiency of winterkill protection management at the
locality. Although our data are limited and represent only one season, they provide valuable
new information about catfish winter behaviour.