Mexican tetra - Astyanax mexicanus
The Mexican tetra (Astyanax mexicanus) is a freshwater fish of the characin family (family Characidae) of order Characiformes.[1] [2] The type species of its genus, it is native to the Nearctic ecozone, originating in the lower Rio Grande and the Neueces and Pecos Rivers in Texas as well as the central and eastern parts of Mexico.
Growing to a maximum overall length of 12 cm (4.7 in), the Mexican tetra is of typical characin shape, with unremarkable, drab coloration. Its blind cave form, however, is notable for having no eyes and being albino, that is, completely devoid of pigmentation; it has a pinkish-white color to its body.
This fish is reasonably popular among aquarists. This is especially true of the blind cave form.
A. mexicanus is a peaceful species that spends most of its time in the mid-level of the water above the rocky and sandy bottoms of pools and backwaters of creeks and rivers of its native environment. Coming from a subtropical climate, it prefers water with 6.0–7.8 pH, a hardness of up to 30 dGH, and a temperature range of 20 to 25 °C (68 to 77 °F). In the winter it migrates to warmer waters. Its natural diet consists of crustaceans, insects, and annelids, although in captivity it is omnivorous.
The Mexican tetra has been treated as a subspecies of A. fasciatus, the banded tetra, but this is not widely accepted.