These are a more sincitive fish and require a well established aquarium with constant water peramiters. I've never known this catfish to be a "schooling" fish. I've had 1 to 6 in many tanks before without issue.
Pitbull Pleco is another smaller Pleco. It gets a little bigger (maybe a half inch bigger) and buffer than the Oto cat. Very nice algae eater...
Fishless is right, they need to be in groups of 5+.
They are shy. They are quite hard to get settled in. They have to have a well established tank with lots of plants and algae. In stores they are very stressed and tend to be starving. You'll have to observe them in the store very carefully and choose the healthiest ones. And they still have a good chance to die. Usually if the survive for a month, they are settled and they'll be fine.