X-ray fish, also called the X-ray tetra, is a small, semitransparent freshwater fish of South America. The X-ray fish has bands of yellow, black, and white on most of its fins. It has a reddish tail fin and often a black spot on the front-center of its body, behind the eye. Adults may reach nearly 1 3/4 inches (4.5 centimeters) in length. Males are generally smaller and thinner than females.
The X-ray fish is found widely in the Amazon and Orinoco river basins of South America. It also inhabits the coastal rivers of Guiana. The fish lives in a relatively wide range of conditions, including slightly brackish (salty) waters.
The transparency of the X-ray fish helps it to hide from predators (hunting animals). The fish is transparent because many of its body tissues are arranged in a way that minimizes the scattering of light. Maintaining the shape of these tissues requires energy. Thus, as in other transparent fish, only living tissues are transparent. Dead X-ray fish turn yellow.
X-ray fish prefer to hide in vegetation along the edges of forest streams and small rivers. The fish often gather in large shoals (groups). X-ray fish flick their fins as a visual alarm. This behavior warns other X-ray fish of the presence of predators. Like many tetras, X-ray fish feed on a variety of water insects and other small animals.
X-ray fish may live up to five years in an aquarium. In the wild, their lifespan is somewhat shorter. The fish usually breeds in its third year of life.
