An odd species of tetra from the Congo, these are a pterygophagous species, ie they specialise in eating the fins of other fish!
Most hobbyists and stores sustain these animals by leaving them in a tank full of long-finned fish such as Goldfish. The tetras do not kill the goldfish, and once the fins are sufficiently depleted they are swapped out for a new group and left to recuperate. Rinse, and repeat.