X-Ray Tetra

X-Ray Tetra Introduction

Pristella maxillaris, the only species in the genus Pristella, is commonly known as the X-Ray fish or X-Ray Tetra because of its translucent body. The X-Ray Tetra is a small species of schooling fish that is naturally found in the Amazon rivers coastal waters in South America.

They were first described by Ulrey in 1894 and have since become one of the most popular freshwater fish kept in artificial aquariums today. Although the X-Ray Tetra is the only known species in its genus, it is closely related to other small and colorful South American fish, including the nearly 100 other tetra species.

The most distinctive feature of the X-Ray Tetra is the translucent layer of skin that covers its small body, allowing the fish backbone to be clearly seen. The scales of the X-Ray Tetra are a silvery-yellowish color that is very faint, looking almost golden in some lights.

The X-Ray Tetra also has a re-tipped tail and strikingly striped dorsal and anal fins that are yellow, black and white in color. This is a relatively small species of fish that actually has a bony internal structure known as the Weberian apparatus, which is used in picking up sound waves, and contributes to their acute sense of hearing.

(this bony structure is also found in many of their relatives) Females are generally slightly larger and rounder than the slenderer males, although the two are very similar in appearance.

Keywords to learn

Translucent: allowing light, but not detailed shapes, to pass through; semi-transparent.

Crustacean: An arthropod of the large, mainly aquatic group Crustacea, such as a crab, lobster, shrimp, or barnacle.

About Me

Hey Kids, my name is Xena the X-Ray Tetra and I am very happy to meet you. Learn more about me and my species @ www.kids.nationalgeographic.com

Key X-Ray Tetra Data

  • Order:
  • Lifespan:
    2 – 5 years.
  • Class:
  • Scientific Name:
    Pristella maxillaris
  • Mass:
  • Length:
    3.2cm – 5cm. (1.6in – 1.9in)
  • Region found:
    Brazil, Guiana, Guyana, & Venezuela.
  • Population Status:
    Not listed.
  • Current population trend:
  • Diet:
  • Sexual maturity:
    5 – 8 months.

There are a many different types of tetra fish, however the X-Ray Tetra are special. They are invisible!! Well not quite but close.

Now that you know more about the X-Ray Tetra by learning the key data above, be sure also to check out the fun facts. When you are finished learning the facts, try answering the questions in the Q&A corner on the bottom right side of the page.


Download questions about X-Ray Tetra here: X Ray Tetra (answers are on this page)



X-Ray Tetra Fun Facts for Kids

  • # 1. During the rainy season, X-Ray Tetra return to the flood-lands to spawn. Unlike many similar fish who give birth to live young, the female X-Ray Tetra lays between 300 – 400 eggs by scattering them amongst the vegetation. (when she is ready to spawn, the see-through skin means that her eggs can also be easily seen) X-Ray Tetra fry begin to hatch as early as 24 hours later and become free swimming within a few days. Once able to swim, the small and dull white young, are able to find better food sources and soon develop their characteristic adult markings. X-Ray Tetra usually live for three or four years in the wild but can get to older ages in captivity.
  • # 2. Like many other small species of fish that live in the Amazon, X-Ray Tetra is an omnivorous animal whose diet is made up of both animals and plants. X-Ray Tetra primarily hunt worms, insects and small crustaceans that live close to the river bed and their fry tend to feed on Insect larvae. Although they are also known to supplement their diet with aquatic plants, they are predominantly micro-predators that feed on small invertebrates.
  • # 3. In artificial communities, X-Ray Tetra need a variety of food sources including Brine Shrimp and Bloodworm alongside the standard flakes and pellets to ensure that they have a fully nutritious diet.
  • # 4. The small size of the X-Ray Tetra means that they should not be kept in the same aquarium as larger, predatory fish, but will co-inhabit the tank peacefully with other small, schooling fish that pose them no threat. In the wild, X-Ray Tetra are preyed upon by a number of aquatic predators including larger fish and frogs, and are also threatened by birds and snakes if they are closer to the water’s surface. Populations are thought to be the most under threat from the rising levels of pollution in the water and habitat loss in general.
  • # 5. The Weberian apparatus (the bony structure) in the X-Ray Tetra’s body works by transmitting sound waves through their vertebrate, that have been received by the swim bladder and are then taken to the inner ear, meaning that the X-Ray Tetra has excellent hearing. The transparency of their skin is thought to be a form of protection as predators find it much harder to spot them (along with their light yellow markings) amongst the dense vegetation, and shimmering water.

Q&A Corner

  • # 1. What color are the X-Ray Tetras scales?
  • # 2. Which is larger male or female X-Ray Tetras?
  • # 3. When does the X-Ray Tetra reach sexual maturity?
  • # 4. How many eggs does the female X-Ray Tetra give birth to?
  • # 5. Why are the X-Ray Tetras under threat?


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