The diel activity of crucian carp, Carassius carassius, in relation to chemical cues from predators

Chemical cues from piscivorous fish and prey alarm substances often cause r apid fright responses in prey. However little is known of how piscivore-rel ated chemical cues affect prey behaviour over periods longer than a few hou rs. Here we have investigated how chemical cues from piscivorous northern p ike, Esox lucius, affect habitat choice and diel activity of crucian carp, Carassius carassius, over an extended period 11 days. At the beginning of t he experiment control fish were nocturnal while fish in the pike cue treatm ent were aperiodic. After 11 days, control fish had become more strongly no cturnal and displayed two activity peaks during early and late night wherea s fish in the pike cue treatment were still aperiodic with no activity peak s. Habitat choice was aperiodic in both treatments throughout the experimen t. In both treatments, more fish were found in the vegetation zone than in the open habitat. This was most pronounced when pike cues were present. The se results demonstrate that short-term anti-predator responses to chemical cues from predators can translate into long-term adjustments of diel period icity. Further, the results did not support the idea that crucian carp shou ld switch to nocturnal activity in response to visually hunting predators. Control fish were nocturnal and chemical cues from pike did not make this p attern more pronounced.