http://dx.doi.org/10.1590/1519-6984.16614 Original Article Spatial variations in fish assemblage structure in a southeastern Brazilian reservoir B. O. Sanchesa, R. M. Hughesb, D. R. Macedoc, M. Callistod and G. B. Santosa* aPrograma de Pós-graduação em Zoologia de Vertebrados, Pontifícia Universidade Católica de Minas Gerais – PUC Minas, Avenida Dom José Gaspar, 500, CEP 30535-610, Belo Horizonte, MG, Brazil bDepartment of Fisheries & Wildlife, Amnis Opes Institute, Oregon State University, 200 SW 35th Street, Corvallis, OR 97333, USA cInstituto Brasileiro de Geografia e Estatística – IBGE, Rua Oliveira, 523, CEP 30310-150, Belo Horizonte, MG, Brazil dDepartamento de Biologia Geral, Universidade Federal de Minas Gerais – UFMG, CP 486, CEP 30161-970, Belo Horizonte, MG, Brazil *e-mail:
[email protected] Received: August 14, 2014 – Accepted: October 30, 2014 – Distributed: February 29, 2016 (With 3 figures) Abstract We assessed the fish assemblage structure and composition of Nova Ponte Reservoir (Araguari River, Upper Paraná Basin, Brazil). We observed significant differences in abundance (p = 0.0003), richness (p = 0.0005) and diversity (p = 0.02) between lacustrine and riverine zones of the reservoir. Nine species were significantly more abundant in the riverine region: Astyanax altiparanae, Astyanax gr. fasciatus, Galeocharax knerii, Hoplias intermedius, Hypostomus sp., Leporinus friderici, Leporinus obtusidens, Pimelodus maculatus and Schizodon nasutus. The results indicated a longitudinal gradient in the composition and abundance of fishes in Nova Ponte Reservoir, reinforcing the importance of freely flowing riverine reaches for conserving native neotropical ichthyofauna and reflecting the strong adaptation of these species to riverine systems. Keywords: fish community, Upper Paraná River Basin, spatial gradient.