The brilliantly colored cardinal tetra features a stunning neon blue stripe that spans from its nose to tail, complemented by a vivid red stripe just below. The red coloration extends all the way to the tail, which is transparent along with the other fins. The fish's underbelly is a soft white, creating a striking contrast against its colorful markings.

One key characteristic that distinguishes the cardinal tetra from its close relative, the neon tetra, is that the red color band of the cardinal tetra spans the entire length of its body, whereas in the neon tetra, the red band runs only from the mid-body to the tail. For adult cardinal tetras to display their most vibrant colors, they require very soft and acidic water.