Morphology and habitat use by fishes of the Rio das Velhas basin in southeastern Brazil

We analyzed the morphology and habitat use of 16 small-sized fish species that are abundant in the Rio das Velhas basin using 17 morphological attributes. Habitat use was characterized in terms of the species mean density considering three hydraulic factors: substrate, water depth and mean water velocity. The distribution of species within the morphological space demonstrated congruence between the morphological attributes of a species, and their occupation of vertical microhabitats. Based on this data, the species could be classified as benthic A, benthic B or nektonic zone-dwelling species. Benthic A and B species differed mainly in relation to their body shapes, which were fusiform or depressed, respectively. Generally, habitat selection by each species was related to certain hydraulic factors, water velocity in particular. Siluriformes generally had morphological or behavioral adaptations to live in fast flowing habitats, and they were found more frequently than Characiformes in microhabitats with greater water velocities. Benthic species were the most selective with respect to substrate type. Between congener species, the habitat use of Serrapinnus heterodon and Serrapinnus piaba greatly overlapped, but these species were separated in morphological space. In contrast, Characidium species were closely related in morphological space but had great habitat segregation. Fish requirements and habitat use are poorly understood but are important to species management and habitat restoration.