Meal Scheduling Modulation of Circadian Rhythm of Phototactic Behaviour in Cave Dwelling Fish

Phototactic responses of three groups, each of 16 cave fishes, were observed at 4-hr intervals beginning at 0900, following S days of acclimation inside specially designed aquaria. The latter consisted of two parts, a photic zone and an aphotic zone. The first group of fishes were fed ad libitum, while the second and third group of fishes were fed with minced mutton and/or liver delivered in the photic zone between 0700-1100, and in the aphotic zone between 1900-2100. The percentage of fishes present in the photic zone at a given time was used as a measure of their phototactic responses. Single cosinor analysis of these data has revealed, for the first time, a circadian rhythmicity in the phototactic behaviour of a cavernicolous organism. However, imposition of restricted feeding schedules shifted the peak time of the circadian rhythm in phototactic responses. Meal scheduling may thus be an effective synchronizer for this behavioural rhythm.