Pristella maxillaris

Pristella maxillaris is a species of characin in the genus Pristella, and is commonly known as the X-ray fish or X-ray tetra because of its translucent body. It is a widely distributed and adaptable fish, found in the Amazon and Orinoco basins, as well as coastal rivers in the Guianas in both acidic and alkaline waters. Unlike most other characins, it is tolerant of (and sometimes found in) slightly brackish water. It is small (up to around 5 cm or 2.0 in in length) 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.