X-Ray Tetra Facts, Pictures & Information

X-ray tetra facts and pictures. Discover a small fish from South America that is popular among aquarium owners due to its distinctive transparent appearance…

X Ray Tetra Facts at a Glance

Other Name(s): X-ray fish, goldfinch tetra, signal tetra

Scientific name: Pristella maxillaris

Type of Animal: Fish

Animal Family: Characidae

Where Found: Amazon & Orinoco Basins, coastal rivers and swamps of northern South America (and home aquariums throughout the world)

Length: 4 to 4.5 cm (1.57 to 1.77 in.)

Conservation Status: Unassessed

X Ray Tetra

X Ray Tetra


The X-ray tetra is a small fish, growing to a maximum length of around 4.5 cm (1.77 in.). Females are slightly larger and heavier than males.

The species gets its name from its transparent skin and flesh, through which its internal organs and skeleton can be seen. Looking at an X-ray tetra is like looking at an X-ray of a normal fish!

x-ray tetra close-up
Photo: Richard Bartz, Munich Makro Freak [CC BY-SA 2.5]
Both the X-ray tetra’s dorsal (upper front) and anal (lower hind) fins are black with a yellow strip near the body and a white tip. The caudal (tail) fin is translucent and faint red.

The fish’s coloration is reminiscent to that of a goldfinch, and the species is sometimes called the goldfinch tetra or water goldfish.

Family & Related Animals

The X-ray tetra is a member of the fish family Characidae. Members of this family are known as characids. They are (mostly) freshwater fish that are found in the rivers of the Americas.

Classification of this group of fishes is constantly changing. Related fish that were once included in the family Characidae, but are now placed in their own families, include the pencilfish, dogtooth characins (also known as vampire tetras), and the fearsome piranhas.

Red bellied piranha
Red bellied piranha

The group of fishes known as tetras contain not just the members of the family Characidae, but also those of several other fish families, including Lebiasinidae and Alestidae (African tetras).

Tetras can be recognized by their flat bodies, forked tails, long dorsal fins and anal fins that stretch from midway along the underside of the body to the start of the tail fin.

Other well-known and popular tetra species include the neon tetra, glowlight tetra, bloodfin tetra, serpae tetra and diamond tetra.

Where Is The X-Ray Tetra Found In The Wild?

pristella maxillaris / X ray tetra
Photo: Debivort at the English Wikipedia [CC BY-SA 3.0]
The X-ray tetra is found in the wild in South America. It is present in both the Amazon and Orinoco rivers and their tributaries. It is also found in coastal rivers and swamps in Venezuela, Guyana, Suriname and French Guyana.

Unlike most other tetras, the X-ray tetra is able to live in water that is slightly brackish (salty), although it is mostly found in freshwater habitats.

The X ray tetra is a popular fish in home aquariums, and is bred in high numbers for this purpose.

Behavior & Diet In The Wild

The X-ray tetra lives in large shoals. In the wild it feeds on small insects, worms, crustaceans and planktonic animals.

Keeping X-Ray Tetras

The X-ray tetra is relatively easy to look after. This, and its attractive looks make it a very popular aquarium fish. It is non-aggressive and hardy, although it won’t fare well alongside larger and more aggressive species. As a shoaling fish, the X-ray tetra should be kept in groups of at least 6, preferably over 10.

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