MICROHABITATS AND DIEL DOWNSTREAM MIGRATION OF YOUNG GRAYLING (THYMALLUS-THYMALLUS L)

1. Microhabitats chosen by young grayling (Thymallus thymallus L.) were investigated by electrofishing. The first feeding habitat was marginal areas where water velocity did not exceed 15 cm s-1. Fry fed on drift in the first 10 cm of the water column below the surface. This location was very stable during the first weeks of growth (mid-April to mid-May). When they were 3-3.5 cm long, fry began using benthic areas and gradually moved away from the banks towards the channel. 2. A downstream migration was noted from the beginning of emergence (mid-April) to the end of May. This mainly nocturnal movement involved all fish sizes and caused a complete removal of young-of-the-year by June from the spawning tributary.