Astyanax courensis belongs to the A. scabripinnis species complex and is distinguished from other species of this complex by the number of scale rows between lateral line and pelvic fin origin (3-4 vs. 5-6), except from A. brachypterygium, A. burgerai Zanata & Camelier, A. goyanensis, A. intermedius Eigenmann, A. jenynsii, A. microschemos, A. rivularis Lütken, A. totae, and A. varzeae. It differs from A. brachypterygium, A. goyanensis, and A. totae by head length (24.9-28.2% SL, mean = 26.6 vs. 27.8-33.2, mean = 29.9, 27.7-32.3, mean = 31.6, and 27.9-32.8, mean = 29.7, respectively), and by the number of humeral spots (1 vs. 2, except in A. totae, which has one). It differs from A. burgerai and A. intermedius by shape of the dentary teeth (abruptly decreasing in size after fourth tooth vs. teeth gradually decreasing in size posteriorly), and orbital diameter (24.9-31.9% HL, mean = 27.9 vs. 34.6-40.6, mean = 38.0, 32.5-47.8, mean = 39.0, respectively); from A. jenynsii by the number of branched anal-fin rays (15-17, mean = 15.8 vs. 13-15, mean =14) and upper jaw length (40.6-50.0% HL, mean = 44.9 vs. 35.9-39.5, mean = 37.4); from A. rivularis by body depth (27.4-33.1% SL, mean = 30.5 vs. 35.0-46.0, mean = 40.3), and by the number of humeral spots (1 vs. 2); from A. varzeae by the number of lateral line scales (35-36, mean = 35.4 vs. 37-42, mean = 39), caudal-peduncle length (13.6-16.9% SL, mean =15.2 vs. 10.5-13.9, mean = 12.4) and orbital diameter (24.9-31.9% HL, mean = 27.9 vs. 30.9-44.5, mean = 37.9). Furthermore, it differs from A. microschemos and A. totae by the number of maxillary teeth (1 vs. 2-3 and 2-5, respectively). Astyanax courensis differs from only sympatric Astyanax species, A. goyanensis, by the number of pelvic-fin rays (8 vs. 7), and number of maxillary teeth (1 vs. 2-5), and by prepectoral distance (23.7-27.8% SL, mean = 26.4 vs. 27.7-32.0, mean = 30.4) (Ref. 84461).
||The collection locality is around 1135 m above sea level, rio dos Couros in that point has moderate riparian vegetation and it is typically between 10 and 15 m wide, and 1.5 m deep. Although presenting some rapids, the water is clear, the substrate has stones, rocks, and some stretches with mud. Most of the specimens were collected on the stretch downstream from the waterfall, a few specimens on the stretch upstream of waterfall. Only 4 species were collected syntopically with A. courensis: Characidium stigmosum,
C. aff. zebra, Gymnotocinclus anosteos and Trichomycterus sp. The stomach contents of five specimens consisted of Plecoptera, Trichoptera, Chironomidae (Diptera), authochthonous and allochthonous insects, and digested vegetal organic matter; these stomachs were partially full (Ref. 84461).