Above is a picture of an otocinclus catfish. It is a small (2") algae-eating fish which is perfect for the tropical freshwater aquarium. It is a diligent worker, doesn't have an aggressive bone in its body, and is fun to watch interact with others in a group. Other names for otocinclus are "otos", or "dwarf suckermouth catfish".
Also notice the nice green poop. Otocinclus should be constantly pooping. In fact, most fish from the family Loricariidae are big poopers. Since otocinclus are mainly herbivores they need massive quantities of greens to keep them healthy. The best form of this is the soft green algae that is sometimes difficult to see. A fat oto is a happy oto! If your oto is slim in any sense of the word then you need to supplement their diet with zucchini or spinach, or figure out a way to grow more algae!
from the net...