Patterns of amplified DNA fragments flanked by (GGAC)n microsatellites, obtained by single primer amplification reaction (SPAR), from 198 Gymnotus specimens (Pisces: Gymnotiformes) sampled from 8 southeastern Brazilian river basins were analyzed. The species studied were Gymnotus carapo, G. pantherinus, G. inaequilabiatus, and G. sylvius. The indirectly obtained patterns reflected the distribution of simple sequence repeats in the nuclear genome of the specimens. Species-specific patterns of DNA amplification were found and were useful for the analysis of the geographic distribution of Gymnotus species. Monomorphic patterns were found in G. carapo, G. pantherinus, and G. inaequilabiatus. Three polymorphic patterns were found in G. sylvius populations. The SPAR technique could be a useful molecular tool in conservation programs involving communities of neotropical freshwater fish.
