Diel locomotor activity and shelter use in the Patagonian catfish Hatcheria macraei under experimental conditions.

Diel locomotor activity and shelter use was experimentally evaluated in Hatcheria macraei under three different light regimens: natural and inverted photoperiods, and during constant darkness. The results demonstrate clear nocturnal activity and highlight the negative phototactic behaviour of H. macraei, proving that light is the external factor that triggers the seeking of shelter and the subsequent hiding action. Locomotor activity was maximal in darkness, intermediate at dawn and dusk, and minimal (maximum shelter use) in full light. During free-running experiments (i.e. constant darkness) H. macraei continued to exhibit the same diel pattern of resting (or hiding) and swimming as under natural light conditions. Nocturnal activity and negative phototactic behaviour appear to be important mechanisms which have enabled H. macraei to withstand the effects of salmonid introduction in lotic environments where other native fishes have suffered negative effects. [ABSTRACT FROM AUTHOR]