Looks like an astyanax tetra of some kind. Given the location it may be a Mexican tetra. These tetras get around 6" full grown and are very nippy. They are the only native tetra to the U.S.
I have two spot astyanax which are found in CA and SA. Notice the similarities.
No problem. Did you get a bunch of them? I'd keep them in schools. They are very rare. Some people who snorkel in Mexico hate them because they will bite lol.
I did get a bunch but threw them all back. I meant to only keep the green sun fish but this one slipped in. I will probably try to get more next time I go to the ranch.