Introduction
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".
The picture above is of a nice fat female, if you click on the picture and look carefully you can actually see an egg or two right near its left ventral fin. I guess I came close to breeding these fish when the picture was taken but I never saw any fry. I hope that will change with my recent stock.
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!
Here are some general links I've found on the web about otocinclus:
"Little Monkeys" article at planetcatfish.com
Another general care article at webwebmedia.com
Catfish of the Month article at planetcatfish.com
Robyn's Oto Page
Teeny Weeny Algae Eaters by Lynn McMullen
Comments from owners of otocinclus catfish at aquahobby.com