Spatial distribution of drifting cyprinid fishes in a shallow lowland

With 3 figures and 4 tables Abstract: We investigated downstream drift of the early developmental stages of cyp-rinid fishes in a shallow lowland river to ascertain the spatial dynamics of this mode of transport. Drift density and mean body size were compared among four sampling sta-tions positioned at different distances from the riverbank through a series of diel sam-pling periods. Common bream (Abramis brama) was the dominant species (76%), fol-lowed by silver bream (Abramis bjoerkna) and roach (Rutilus rutilus). Ninety-five per-cent of drifting fish were larvae. Most fish drifted 1 to 3m from the shore, at a max-imum density of 131 fish 100m–3. Relatively few fish drifted in midchannel and most fish drifted at night. Body size of drifting fishes was positively correlated with distance from the bank. Consistent results were obtained from analysis of developmental sta-ges, with younger larvae drifting near to the bank and older larvae and early juveniles drifting in midchannel. We propose that the spatial distribution of drifting fish is linked to their swimming ability and fish larvae may enter the river current as a means of ac-tive transport. Key words: downstream drift, early life history, larval dispersal, fish migration, young-of-the-year fish, 0+ juvenile fish