Astyanax acatlanensis is distinguished from its congeners in inland central Mexico by the following characters: supracephalic profile, usually concave (vs. usually convex); modally 12 (modally 11-11.5) predorsal scales; modally 15.5 or fewer scales around caudal peduncle (vs. modally 16 or more); 10 or more procurrent unsegmented caudal fin rays on dorsum (9 or fewer

in A. rioverde); head short, mean 23.8% SL (mean 24.6% or higher in A. mexicanus, A. rioverde and A. salvatoris); sides of anterior fontanel, straight (convex, in A. rioverde); ascending vs. descending arms of premaxilla, subequal (vs. dentigerous longer); infraorbital IV, square with projections (rectangular in A. rioverde); and opercle dorsal edge, convex (obtuse in A. rioverde and A. salvatoris) (Ref.118583).