Ecomorphology and diet of two species of Acestrorhynchus from Brazilian Northeast
Acestrorhynchus falcatus (Bloch, 1794) and A. heterolepis (Cope, 1878) are two species frequently found in rivers from Baixada Maranhense, Maranhão State, northeastern of Brazil. The ecomorphological adaptations of these species were studied based on a collection of 445 specimens using morphometric tools. Seventeen landmarks were defined on the lateral side of the individuals and digitalized by the TPS Dig program. The data matrix was submitted to a Relative Warps Analysis (RWA) and a Canonical Variables Analysis (CVA) in order to identify the morphological patterns of each species. In addition, observations about the digestive tract of each species and diet comparison through the feeding ecology are provided. The main differences between A. falcatus and A. heterolepis, as indicated by the analysis, were associated with swimming agility and prey size. A. heterolepis has a shallow body, close to a fusiforme profile, deep caudal fin and low caudal peduncle. In contrast, A. falcatus possesses a shorter head and a lower caudal fin, better adapted to capture small preys and to live in mid-lower region of the water column. According to these traits, the two species probably avoid competition by catching prey of different sizes and using distinct strategies for this procedure.