Daily activity rhythms of the African catfish Heterobranchus longifilis (Clariidae) in an experimental enclosure

¹ University of Liège, Center for Cognitive and Behavioural Neuroscience (B32), 5 Boulevard du Rectorat, 4000 Liège, Belgium
² University of Liège, Laboratory of Fish Ethology, Belgium

Corresponding author: panselme@ulg.ac.be

Received: 4 March 2008
Accepted: 1 September 2008

Abstract

The swimming, air-gaping, and agonistic behaviours of Heterobranchus longifilis (318 ± 67 mm) were examined while fish were in a fasted state under 12L:12D and variable group size (2, 5, 10 and 15 fish) in a 1000-L aquarium. Fish exhibited a predominantly nocturnal activity pattern independent of group size. A diurnal peak of activity occurred, however, at the usual feeding time. A reduction in frequency of agonistic interactions was observed in larger groups. Five fish were then observed under 72L:0D and 0L:72D. The nocturnal activity pattern remained, contrary to the diurnal peak, and was independent of the duration of illumination or darkness. These results suggest the absence of biological clock in H. longifilis, although fish may somehow be influenced by past feeding experience. Behavioural plasticity in this species may provide potential for aquaculture in northern latitudes.