Restoration of a river backwater and its influence on fish assemblage

The development of fish assemblage in a restored river backwater (Kurfürst backwater, Morava River, Czech   Republic) was monitored over a six-year period from its restoration. The structure of fish assemblage remained similar throughout the years. Species richness of adult fish increased from twelve species during the restoration to 20 after it. Initially steady fish abundance (mean 52.3–98.1 inds/ha) and biomass (mean 5.8–7.6 kg/ha) increased significantly in 1999 five years after restoration (576.9 inds/ha and 23.3 kg/ha, respectively). The main resident species were pike Esox lucius, roach Rutilus rutilus, rudd Scardinius erythrophthalmus and perch Perca fluviatilis. High abundance of bleak Alburnus alburnus and chub Leuciscus cephalus was related to their spring spawning period. The structure of the 0+ fish assemblage was similar throughout the years, with chub and bleak prevailing during the restoration, and roach, chub and rudd after it. The number of 0+ species increased from seven to 17. The monitoring documented that the restoration could be considered as beneficial for the fish assemblage. Habitat development of the backwater is likely to influence its current value as a refuge, spawning site and nursery for local fish populations.