Astyanax altior, the Yucatán tetra, is a species of freshwater ray-finned fish belonging to the family Acestrorhamphidae, the American characins. This fish is endemic to the Yucatán Peninsula of Mexico. It largely inhabits the cenotes (water-filled sinkholes) of the region, and can tolerate water of limited salinity, though it largely prefers freshwater. Its diet includes plant matter and invertebrates, and there may be an element of cannibalism involved.

It bears a genetic and morphological resemblance to congener Astyanax aeneus, with which it was once considered synonymous; however, more recent ecobiological assessment has determined that the two are separate.

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