Functional link between foraging performance, functional morphology, and diet shift in roach (Rutilus rutilus)

This study explores how feeding performance (size-dependent attack rate) and the diet shift from zooplankton to benthic macroinvertebrates in the fish species roach (Rutilus rutilus L.) is related to changes in functional morphology over ontogeny. The morphological changes included overall body shape and structures of the feeding apparatus. The foraging performance of roach on zooplankton, as a function of size, was hump-shaped with a maximum of ~160 mm, and the diet shift took place around 150 mm. Over ontogeny, roach body shape gradually changed from fusiform into high-bodied. The second principal component (PC2) of the feeding apparatus had a U-shaped relationship with body size, with a minimum at 140-mm total length, which is the inverse of that found for the foraging performance on zooplankton. We suggest that changes of the feeding apparatus affect prey intake during the early zooplanktivorous phases and at the final benthivorous feeding stage, whereas prey retention ability limits the maximum intake rate at a later phase of the zooplanktivorous feeding stage. Our results also suggest the presence of both positive and negative correlations in morphology between the feeding niches, which point to the occurrence of morphological trade-offs within ontogenetic niches