A. aeneus before being given proper species designation. As such, A. aeneus is regarded as a cryptic species - that is, more than one species currently considered synonymous. It is at the center of a species complex bearing its name. Within Astyanax, there are three subgenera - Astyanax strictu sensu, Poecilurichthys, and Zygogaster. A. aeneus belongs to the first. Etymology The word "aeneus" means "bronze" or "brazen" in Greek, referencing the brownish back. The specific epithet "aeneus" is not uncommon in taxonomy; consider Anolis aeneus, the bronze anole, or Molothrus aeneus, the bronzed cowbird. The specific reason for the genus name Astyanax is unknown, but the origin is in Homer's Iliad. Astyanax was a warrior of Troy, and was the son of famed warrior Hector. One possible reason for the allusion is the large, armor-like or shield-like scales of type species A. argentatus, which is now known as A. mexicanus. Distribution Astyanax aeneus is a widespread species. In Central America, countries include Mexico, in the rivers Papaloapan and Colima, Panama, in the rivers Cocle del Norte and Tabasara, and Honduras, in the Choluteca river. South American countries with populations of A. aeneus include El Salvador and Guatemala. While largely freshwater, A. aeneus demonstrates no preference for one specific habitat or another. It is found in fast-flowing rivers, stagnant swamps, sizable lakes, and even the occasional brackish lagoon. Whatever the case, it tends to linger in the stretch between the middle of the water column and the substrate. Because of its variable environment, A. aeneus is an adaptable species. One example of this is that the lower lip can expand to increase the surface area of the interface between water and air as a part of aquatic surface respiration (ASR) in hypoxic environments. (A specific morphological variation in response to an environmental stressor is referred to as an ecophenotype.) This specific adaptation once led to the mistaken designation of a new species, A. armandoi, which has since been synonymized with A. aeneus. Astyanax aeneus has also adapted to cave environments in a similar manner to its more well-known cousin, the blind Mexican cavefish (Astyanax mexicanus). Changes include "eye and pigmentation regression, as well as modifications in brain morphology, behaviors, heart regenerative capacity, metabolic processes, and craniofacial organization" (as described by geneticist William R. Jeffery). There are at least two populations of A. aeneus that are stygobitic (living solely in underground water