Astyanax tehuacanensis is distinguished from other congenes in central Mexico by the following characters: rays on anal fin, mean fewer than 24 (vs. mean 24 or more in A. aeneus); total gill rakers, mean fewer than 20 (vs. mean 22 or more in A. finitimus); head shorter, mean 21.9% SL (vs. mean 23.8% or more); snout shorter, mean 3.3% SL (vs mean 4.2% or more); interorbital, mean 8% SL (mean 9-10% SL in A. acatlanensis and A. mexicanus); pectoral fin shorter, mean 19.3% SL (vs. mean ca. 21% in A. acatlanensis and A. mexicanus); anterior fontanel longer (vs. shorter); infraorbital II, triangular with an angled base (vs. base convex in A. acatlanensis, A. aeneus and A. mexicanus); epibranchial III, distal segment straight (vs. curved in A. finitimus and A. mexicanus); first dorsal pterygiophore, dorsal edge angled (vs. curved in A. mexicanus) (Ref. 118583).