The Mexican Tetra is one of the most scientifically fascinating fish in the aquarium hobby, being the only tetra with both a surface-dwelling sighted form and a cave-dwelling blind form within the same species. In its normal form, it is a robust, attractively silver-bodied fish with a slightly compressed shape and a bold personality. The blind cave form is eyeless and pinkish-white, having lost its eyes and pigmentation through evolutionary adaptation to permanent darkness. Both forms are popular in the hobby for different reasons — the sighted form for its hardiness and wide parameter tolerance, and the blind form for its scientific novelty. Native to river systems of Mexico and southern Texas, the Mexican Tetra is adapted to a wider range of water conditions than most of its South American relatives, tolerating harder, more alkaline water and cooler temperatures. This makes it particularly suitable for community tanks where tropical conditions cannot always be maintained. It is generally peaceful but may occasionally nip the fins of long-finned or slow-moving tankmates, so careful selection of companions is advised. A schooling species that appreciates groups of six or more.
