I dont know about shoaling, but the 4 corys I have atm hang out together a lot. They follow each other around. Tend to find them resting/sleeping(?) in the same spot together. They seem happy to me, very sociable with one and other. Anyone else had problems keeping mixed species of cory? I could keep them in pairs, but I couldnt have five of each species of the ones I have - I dont have the room. argh..