Convict Blennies (Pholidichthydiae) live in small holes in the sand and rocks. At first they live on only zooplankton, but as they become larger they also start eating fish and crustaceans.
Provided with the right environment these fish are a nice and unique addition to an aquarium.
One should be aware that these fish dig into the bottom so that sand and debris whirls around in a tank. If one wishes an aquarium where the debris does not accumulate in one place, this is the obvious choice.