Astyanax epiagos can be distinguished from most of its congeners and from all other Astyanax species known from northeastern Brazilian drainages (A. brevirhinus, A. fasciatus, A. intermedius, A. lacustris, A. pelecus, A. rivularis, and A. taeniatus) by a vertically elongated humeral blotch and body highest along vertical through midlength of pectoral fin (vs. distinctly horizontally elongated humeral spot and highest body depth just anterior to dorsal-fin origin in A. lacustris and A. pelecus), absence of dark stripe from humeral region to caudal peduncle (vs. well defined dark midlateral stripe along most of body length in A. intermedius, A. pelecus, A. rivularis, A. taeniatus), 2-4 outer premaxillary teeth and total anal fin rays 17-21 (vs. 5 teeth and 28 anal-fin rays in A. brevirhinus).