Circadian rhythms of locomotor activity in the goldfish Carassius auratus

Locomotor activities in the goldfish Carassius auratus were recorded under light-dark (LD) and constant light regimens. Under LD 12:12, all goldfish adjusted to given LD cycles. Activity patterns were classified into three types: L-type activity during the photophase (83%), LD-type activity both during the photophase and the scotophase (10%), and D-type activity during the scotophase (7%). However, these patterns were not fixed, but flexible. Under constant conditions, goldfish exhibited circadian locomotor activities: The proportions of appearance of circadian rhythms and tau values under constant darkness (DD), constant light (LL, 500 lx) and constant dim light (dimLL, 20 lx) were 57% (24.4 +/- 1.6 h, [mean +/- SE], n = 34), 57% (25.2 +/- 2.5 h, n = 35) and 67% (26.0 +/- 3.4 h, n = 10), respectively. These results indicate that the goldfish exhibit flexibility in phasing of locomotor activity rhythms under LD 12:12. In addition, the coupling between circadian clocks and locomotor activities does not seem strong, although the diel locomotor activity in the goldfish is regulated, in part, by a circadian clock. These results are discussed in context with the structure of the teleostean circadian system.