Food-entrainable circadian oscillator in goldfish: multiple daily feeding times and food-anticipatory activity

摘要

The existence of a food-entrainable circadian oscillator (FEO) was examined in goldfish Carassius auratus. Single goldfish were exposed to light–dark (LD) 12:12 (lights on 06:00–18:00?h) and fed at 12:00?h (phase?I). The photoperiod regime was shifted to constant light (LL) (phase?II). The fish were then fed at 06:00 or at 18:00?h (phase?III), and all fish were fasted (phase?IV). In both groups, three out of eight fish exhibited food-anticipatory activity (FAA) in phases?II and III, the free-running period (τ) of locomotor activity was approximately 24.0?h, and circadian rhythms of locomotor activity started to free-run from the previous FAA in phase?IV, indicating the existence of an FEO. Next, single goldfish were exposed to LD 12:12 and were fed twice daily at 12:00 and 00:00?h (phase?I). The photoperiod regime was shifted to LL (phase?II), and the fish were fasted (phase?III). In phase?II, FAA was observed in three out of six fish for both feeding times. In phase?III, a circadian rhythm of locomotor activity was observed in five fish, and circadian rhythms started to free-run from the previous feeding time (either 12:00 or 00:00?h) in three fish. These results suggest that individual goldfish can remember two daily feeding times.