X-Ray Fish-Facts and Basics, and Description

X-Ray Fish

SpeciesP. maxillaris
NicheAquatic fish
Length1.6-1.9 in (3.2-5 cm)
Lifespan2-5 years
Social StructureSchooling
Conservation StatusNot listed (common)
Preferred HabitatFreshwater ponds and lakes in South America
Average Spawn Size350
Main Prey SpeciesWorms, insects, small crustaceans
PredatorsLarger fish

The Basics of X-ray fish

The X-ray fish is a small aquatic fish native to the Amazon basin in South America. Also known as Golden Pristella Tetra, X-Ray Tetra, and Water Goldfinch, they are known for their translucent skin that allows you to see your organs and skeleton just like on an X-ray.

Description of X-ray fish

The X-ray fish is small at 1.9 inches or less, and the females are slightly larger than the males. It is silvery yellow in color with striking black, white and yellow stripes on the dorsal and anal fin. Its skin is translucent so its internal bone structure is visible.

Although the X-ray fish is the only member of its genus, it is closely related to 100 other species of tetra native to South America. In addition, it is one of the most popular freshwater aquarium species in the world.

Distribution and Habitat

The X-ray fish comes from the Amazon coastal regions of Brazil, Guyana, and Venezuela. They differ from most other tetras in their ability to tolerate brackish water in this region. However, they can also thrive in more typical freshwater environments, usually in streams and tributaries during the dry season and in flooded marshes during the rainy season.

Diet and Predators

The X-ray fish is omnivorous and eats a wide variety of animals and plants. The tetra usually hunts several small species of worms, aquatic insects and their larvae, as well as small shrimp-like animals. They also feed on some plants and algae material to supplement their diet, but they are mostly predators.

Due to their small size, they are also prone to predation by a variety of other species. Larger predatory fish hunt virtually all tetra species, including X-ray tetras. Other animals are also a threat, including amphibians such as frogs, as well as several species of birds and snakes. For this reason, X-ray fish and other similar species are often found in the bottle or at the bottom of the water column to prevent predation by those species that depend on them to swim near the surface to be detected and captured.


During the rainy season, flooded environments allow X-ray fish to access environments that would not otherwise be available to them. This opens up access to hatcheries and increases the availability of food in general. This season, the X-ray fish has evolved to breed.

Courtship and copulation

Unlike related species that give birth to live young, the X-ray fish lays eggs. As grasslands and swamps flood, X-ray fish will spread 300-400 eggs among blades of grass and other vegetation. The fry hatch 24 hours later and swim freely within a few days. At this point, they can tap into more and more food sources and will soon develop their characteristic adult markings that reach sexual maturity around 5-8 months of age. Most people live in the wild for 3-4 years. In an aquarium, some people can live even longer, up to 7-8 years.

Their high reproductive rate is one of the things that makes them such a popular species in aquariums.


Although X-ray fish and their entire ecosystem are still considered common, they remain threatened by unprecedented habitat loss. Much of this is due to the proliferation of illegal logging practices, which often rely on livestock grazing and require the destruction of the rainforest. Along with pollution, this is a very real threat to the entire Amazon rainforest, including the ecosystems where X-ray fish live.

Facts about the X-Ray Fish

The fast reproductive rate and unique appearance of X-ray fish make it one of the most popular aquarium species in the world. However, there are more interesting facts and interesting biological concepts to discover about this species in addition to its famous translucent skin.

The Weberian Apparatus

One of the most fascinating features of this little fish is a bony structure in its body known as the Weber apparatus. This unique structure can be seen in other related species and allows sound waves to pass through your vertebrae and thus be perceived by your inner ear. Depending on the type, the Weber apparatus generally consists of two parts: a moving part known as the pars auditum or Weber’s ossicles, and a supporting structure known as the pars sustainaculum, several uniquely modified anterior vertebrae. Combined with the air in their swim bladder, this unique structure allows X-ray fish to have excellent hearing that can aid in both predator avoidance and prey detection.

Invisibility Cloak

The X-ray fish is known for its translucent skin, hence its common name. But like many morphological features, it has evolved to serve a specific purpose. In this case, they are likely some form of predator avoidance, as they are harder for most of their predators to spot. This is not only due to the transparency of its skin but also to the way it reflects light and shines in a similar way to the aquatic environment in which it is produced. This, combined with their distinctive yellow, black, and white markings on some of their fins, makes them difficult to spot, especially among grasses and other vegetation at the bottom of the waters they normally inhabit.

The World Traveller

Tetras are a very common species in aquariums. Some have unique features like “neon” iridescent stripes on their flanks. Others, like X-ray fish, are known for their translucent skin. In addition, they have a very high productivity rate. Also, they are relatively durable and long-lasting. As long as they are equipped with a large enough aquarium without predatory fish species and a few other species that swarm, they can live up to 8 years with minimal care and attention. In this way, this little fish, which is native to streams and swamps off the coast of South America, was able to find its way around the world.


X-Ray Fish-Facts and Basics, and Description

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