Locomotor Activity Rhythms in Cave Catfishes,Genus Taunayia,from Eastern Brazil (Teleostei: Siluriformes: Heptapterinae)

We studied the locomotor rhythmicity in heptapterine catfishes, genus Taunayia, under free-running conditions (DD) and LD cycles (12:12). Taunayia sp., anophthalmic and depigmented undescribed species from a cave in northeastern Brazil, is the fourth Brazilian troglobitic catfish studied with focus on circadian rhythms. Weak free-running rhythmicity, with absence of significant circadian components, was observed for this species when compared to the epigean, eyed relatives. On the other hand, the studied troglobitic catfishes in general presented significant circadian rhythms under LD cycles, with activity peaks in the night phase probably corresponding to nocturnal activity pattern inherited from their epigean ancestors. However, no residual oscillations were observed after transition from LD to DD. This indicates masking of activity by light-dark cycles. Regression of circadian rhythmicity in the stable, permanently dark subterranean habitat was also observed for other cave fishes. Such regression corroborates the notion that circadian rhythmicity is mainly selected in the epigean environment by ecological factors, namely daily cycles of light and/or temperature.