This species can be diagnosed from all congeners in the rio Uruguay basin, laguna dos Patos and rio Tramandaí systems, except Astyanax ojiara, by the presence of one heptacuspid tooth on maxillary (vs. tri- to pentacuspid teeth). It differs from other congeners, including species complex A. bimaculatus and A. scabripinnis by the following combination of characters: two humeral spots, the first spot vertically elongate; conspicuous caudal spot; 35-39 perforated lateral line scales; 6-7 scale rows between dorsal-fin origin and lateral line; 22-28 branched anal-fin rays; predorsal region scaled; one heptacuspid maxillary tooth; body depth 37.2-44.2% of SL; and head length 22.7-27.3% of SL). It is distinguished from A. ojiara by the head length 22.7- 27.3% (vs. 27.3-29.5% of SL) and by the presence of hooks on anal fin on males (vs. all fins with hooks) (Ref. 94153).