Fright reaction in light and dark: how visual information availability modulates the response to chemical alarm cues

摘要

Alarm cues, released when the skin of ostariophysan fish is injured, elicit striking anti-predator behaviour in conspecifics. Recent evidence Suggests that environmental conditions may affect the response. Light and visibility, and thus the possibility of using the visual sensory channel, may greatly vary in aquatic habitats. The aim of this study was to evaluate the role of visual stimuli in the expression of the response to in alarm cue by Barbus conchonius Hamilton-Buchanan 1822, by analysing both swimming patterns and spatial distribution of the fish. Fish were tested in light or darkness in the absence or presence of a chemical alarm cue. In the absence of light, a simplified fish behavioural response ensued to an alarm cue, i.e., the typical swimming patterns were not performed. However, alteration of fish spatial distribution caused by alarm cue perception was unaffected by the impossibility of relying oil visual cues, as it also occurred in the dark. An increase in cohesion and downward movement in the dark may have an adaptive value in such an environmental condition. However, we hypothesise that swimming pattern alteration does not occur in the dark because it has evolved as a visual signal for conspecifics and/or as all antipredatory response specific for visual hunting predators.