OK, looks like nobody's gonna get it. It's the US's only native characin, Astyanax maxicanus found in the Rio Grande and several southwest Texas drainages (Nueces, Sabinal, Frio, Devils and San Antonio Rivers. While much smaller than their Paranha cousins, they are just as voracious and as you can see, they have the same dentition. I've lost many a fish to them in my aquariums.
