As part of 1111′s A-Z of Creatures. X is for X-ray Tetra. Native to the coastal waters of the Amazon River in South America, the X-ray Tetra is one of the most common freshwater fish kept in artificial aquariums today. They need to get out and see what the real world is all about. If you want to see your favorite animal starting with Y next week (if there is one), drop a comment on the 1111 Animal’s facebook page.