All Fresh Water Fish

Pristella maxillaris

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Pristella maxillaris is the only genus in the family Pristella and is commonly known as the x-ray fish or x-ray tetra because of its highly transparent body.[1] It is a widely distributed and adaptable fish, being found in coastal rivers of Brazil, Guiana, Guyana, and Venezuela in both acidic and alkaline waters.[2] Unlike most other characins, it is tolerant of (and sometimes found in) slightly brackish water.[3] It is small (around 5 cm) and lives in large groups, and males can be distinguished from females by being smaller and thinner than the females. Like most other tetras, it feeds primarily on small insects and planktonic animals.[4]

Pristella maxillaris is a small, adaptable fish that is easily kept in a home aquarium and will eat most prepared foods. It is tolerant of a range of water chemistry values (pH 6-8; hardness up to 20 dGH). It should be kept in groups of at least six specimens and away from aggressive or predatory tankmates, but is otherwise easily kept in the community tank.

Older aquarium books often refer to this species by an obsolete Latin name, Pristella riddlei. Aquarists tend to refer to this fish as the x-ray tetra, though some call it the x-ray fish instead.[5] Other common names include goldfinch tetra, a reference to the similarly coloured goldfinch, and pristella tetra, a modification of its Latin name.[6] A common name that was once widespread but is now rarely used is signal tetra, a reference to the similarity between the yellow and black dorsal fin and the arm of a semaphore railway signal.[7]

The term “x-ray fish” may also be used to refer to glass catfish (Kryptopterus bicirrhis) and Asiatic glassfish (family Ambassidae).