Diel cycle inHoplosternum littorale(Teleostei): evidence for synchronization of locomotor, air breathing and feeding activity by circadian alternation of light and dark

Abstract

Diel cycles of voluntary food intake, locomotor activity and air breathing were studied inHoplosternum littorale(Hancock, 1828), a siluriform fish of the Callichtyidae family living in marshes in northern South America. The study was carried out with six groups of 30 fish each reared in 200‐1 tanks equipped with demand‐feeders and maintained under artificial light‐dark conditions (13.5 L/10.5 D). Feed demand started at dusk and increased throughout the night with a peak between 02.00 and 05.00 hours, during which 3‐h period the fish ate 40% of their total daily ration. There was a marked peak in air breathing and locomotion at dusk, followed by an increased feed intake. When the light‐dark cycle was advanced by 9 h the observed phenomena were the same, so it is assumed that the light‐dark alternation is the synchronizer. In starved fish, locomotor activity and air breathing were increased in the light phase.