One of the most popular fish in the aquarium trade today is the Electric Blue Damsel or Blue Devil Damselfish. Its small size (2”) and its neon blue hue make it so popular. Females are solid blue while males have a tad bit of orange in their fins. The males are usually called Orangetail Blue Damsel. Don’t be fooled by their size though, they are semi aggressive and will nip at other fish. They should be kept in a 30 gallon tank or larger with live rock and coral and places for them to hide. When threatened they will hide in a hole or a crevice and darken to where they are almost black. This is a way for them to hide from predators.
Once they feel comfortable they will return to the open and their color will return to its neon blue hue. They can be territorial of there hiding places and will likely be aggressive towards other fish added to the tank after them unless you provide them with multiple hiding places. They will eat flake and herbivore foods and should be fed often.