Diel distribution patterns of fishes in a temperate large lowland river.

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid-channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes. [ABSTRACT FROM AUTHOR]