Diel rhythms of feeding activity in the European catfish, Silurus glanis.

The diel rhythms of feeding activity of S. glanis held singly or in groups, and with free or time-restricted access to self-feeders is described. It was found that this this species has a strongly nocturnal feeding activity. European catfish can be trained to feed itself by day, but in such case its voluntary feed intake is reduced. When trained to feed by day, they resume their nocturnal behavior in less than 24 h when they have again free access to feed. It is also clearly evidenced that this fish species does not behave the same way when it is isolated from its congeneres rather than when it is maintained in groups, with a tendency to become arhythmic.