Flood duration determines the reproduction success of fish in artificial oxbows in a floodplain of a potamal river

Fish reproduction was studied in six man-made water bodies (borrow pits) adjacent to the channelised Dyje River (Danube basin) over five seasons. Terrestrial vegetation provided spawning and nursery habitats when inundated by raised water levels in the borrow pits (hereafter referred to as 'floods'). The diversity of 0+ fish and the density of 0+ cyprinids (mainly Abramis bjoerkna, Scardinius erythrophthalmus and Rutilus rutilus) in June-October were positively correlated with flood duration in previous months. The density of 0+ Perca fluviatilis was independent of the flood duration. The density of spawners and predators did not influence the diversity of 0+ fish and the density of 0+ cyprinids. Receding flood and associated lack of shelters resulted in decreasing density of 0+ cyprinids, numbers sometimes decreasing to zero. Prolonged floods facilitated the survival of 0+ fish and resulted in high 1+ cyprinid density in the following season. Specific hydromorphological conditions (e.g., the presence of shallow littoral zone or flooded vegetation) are necessary to enable successful spawning and provide shelters for 0+ fish in artificial water bodies.