The pectorals are pinkish and the caudal fin is a warm yellow-gold with a black marginal band. The anal is pinkish to bright red with a black marginal border. Males from the southern range appear to have less red and more yellow in the anal and pectoral fins. The fins of the female are similar to the males, but less intense in color. The pectorals are colorless.
Females are larger and more robust, length up to four inches.
The range of Astyanax fasciatus mexicanus is rather large. As presently understood the native range meets its northern limit in the lower Colorado River drainage of Arizona and New Mexico as well as the Pecos and Nueces Rivers in Texas. The range then extends southward along the Gulf coast to an arm near Laguna de Terminos, Campeche, Mexico and westward in the rivers of the Isthumus of Tehuantepec on the Pacific coast to the Rio Armeria basin in Jalisco, Mexico. As this subspecies readily adapts to clean running waters, bait release introductions in the southern United States are not uncommon. The introduced subspecies range in Texas extends from the northern native boundary to the Wichita and Red Rivers in north-central Texas.