Escape response in the damselfish Chromis cyanea (Pisces: Pomacentridae): A quantitative study

Models of different sizes, shapes, and colours evoked, oriented escape responses in schools of Chromis cyanea in their natural coral-reef habitat. Divers filmed these responses; from the films, the distance of the school from the model at the instant of response (reaction distance) was calculated. For a given model, reaction distance was independent of the speed of the model's approach. Darker coloured models were more effective in causing escape (yielded greater reaction distance) than lighter coloured models, suggesting contrast as an important feature of the stimulus. Larger models were more effective than smaller ones. Habituation to repeated stimuli was absent for inter-trial intervals from 0·5 to 4 min. Natural behaviour of Chromis suggests that cues such as sound, vibration, and details of shape, colours, and motion also play a role in triggering escape.