Morphological variation in riverine cyprinids: a geometric morphometric contribution

This study aimed to contribute to understanding the role of changes in proportions related to variation in size in freshwater fish, particularly Rutilus rubilio, Squalius lucumonis and Telestes muticellus, from central Italy. The ontogenetic shape variation was described by a multivariate regression where the independent and dependent variables were size and a set of shape variables (the latter obtained from geometric morphometric analysis of 16 anatomical landmarks), respectively. Our analyses indicated: (1) proportional ontogenetic changes in several morphometric characters in all populations of the three species; (2) no geographical shape variation for each species; (3) interspecific differences. The main shape changes joining all the populations are the ocular area contraction, the tail peduncle enlargement, and the main changes involving the median body region. The shape variations showed similar modification patterns between R. rubilio and S. lucumonis (the silhouette passed from a streamlined to a more oval and higher shape for both species) and some differences between R. rubilio and S. lucumonis vs. T. muticellus (the latter approaching a more spindle-shaped body). The expression of these allometric trajectories may be associated with age-specific shifts in the ecological niche, optimizing some features such as foraging efficiency and movement.