Daily food-anticipatory activity in golden shiners. A test of endogenous timing mechanisms

Shoals of four golden shiners, Notemigonus crysoleucas, were fed daily at a fixed time, which could be the beginning, middle, or end of a 12-h artificial day, or beginning, middle, or end of a 12-h artificial night, depending on the shoal. Almost all shoals showed food-anticipatory activity (FAA), that is, a gradual increase in locomotor activity near the feeder, starting on average 4.5 h before mealtime. FAA started before the time of lights-on or lights-off even in shoals that were fed 1 h after these times. Increases in activity near the feeder generally did not appear at times unrelated to feeding, except for some shoals that were fed around the time of either lights-on or lights-off and that showed high activity at both of those times simultaneously. When food was withheld but the light-dark cycle was preserved, FAA persisted at the old clock time in 78% of the shoals. When the light-dark cycle was eliminated (fish placed in constant darkness), with or without a concurrent removal of the scheduled feeding, FAA persisted at the old clock time in only 22% of the shoals. These results can be explained by a model whereby the animals possess a circadian oscillator that is entrained by the light-dark cycle, with only weak potential for self-sustainability, and where a representation of the normal phase of feeding can be stored in memory. The possibility that FAA was generated by a food-entrainable oscillator can only be reconciled with the data by postulating that this oscillator is normally linked to a light-entrainable oscillator, and that the damping out of the light-entrained oscillator disrupts the action of the food-entrainable one.