Nematobrycon palmeri, commonly known as the emperor tetra, is a species of characid fish found in the Atrato and San Juan river basins in western Colombia.

[2] The purple hue of these tetras will be more apparent in an aquarium with floating plants on the surface and relatively subdued lighting.

However, this is not always the best indicator as the third prong in males can sometimes be nipped off in competitions with tank mates and more dominant females may sometimes grow this extension of the tail as well.

This species should not be confused with the royal tetra Inpaichthys kerri, whose appearance and alternate common names resemble N. palmeri.

In a large well planted aquarium a single pair of emperor tetras will often breed without any extra stimulation.