Interaction between the roach, Rutilus rutilus, and dace, Leuciscus leuciscus, populations in a river catchment in south‐west England

The ecology of roach, Rutilus rutilus (L.), and dace, Leuciscus leuciscus (L.), populations from different regions of the R. Exe catchment was studied. Dace were the predominant cyprinid in the middle reaches whilst roach dominated in the slow‐flowing lower reaches. Each species showed maximum growth rate and reproductive effort in its preferred habitat, i.e. where it dominated the fish community. The diet of roach consisted mainly of vegetable material, whilst dace were omnivorous. Although each species had a characteristic diet, there was considerable overlap. There was little evidence that variability between regions in growth rates of each species resulted from competition for food.