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

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...