Juvenile wild and hatchery-reared European grayling Thymallus thymallus were tagged with radio-transmitters and tracked in the Blanice River, River Elbe catchment, Czech Republic, to study their behavioural response to stocking and environmental variation. Both wild and hatchery-reared T. thymallus increased their diel movements and home range with increasing light intensity, flow, temperature and turbidity, but the characteristics of their responses differed. Environmental variables influenced the movement of wild T. thymallus up to a specific threshold, whereas no such threshold was observed in hatchery-reared T. thymallus. Hatchery-reared fish displayed greater total migration distance over the study period (total migration) than did wild fish, which was caused mainly by their dispersal in the downstream direction.

Department of Ecology Charles University Faculty of Science Viničná 7 128 44 Prague 2 Czech Republic

Department of Zoology and Fisheries Faculty of Agrobiology Food and Natural Resources Czech University of Life Sciences Prague 165 21 Prague 6 Czech Republic

Institute for Environmental Studies Charles University Faculty of Science Benátská 2 128 01 Prague 2 Czech Republic

University of South Bohemia in České Budějovice Faculty of Fisheries and Protection of Waters South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses Zátiší 728 2 389 25 Vodňany Czech Republic

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Is it possible to contribute to the recovery of European grayling (Thymallus thymallus, Salmonidae) populations by stocking cultured brood fish in the pre-spawning period?

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