This is a very broad category covering thousands of species globally, from the tiny South American Corydoras to the massive Red Tail Catfish. The most popular exotic groups are Corydoras, Plecos (Plecostomus), and Synodontis (Upside-Down Catfish).
Exotic Catfish
Size/Tank: Ranges from 1-inch (Corydoras) requiring small community tanks to 4-foot (Red Tail Catfish) requiring massive custom ponds. Aggression: Varies wildly. Most small species are peaceful community fish, while large species are opportunistic predators that will eat any fish that fits in their mouth. Care: Almost all species prefer a soft, fine sand substrate to protect their sensitive barbels. They are primarily bottom dwellers and need plenty of caves, driftwood, and secure hiding spots. Filtration is always critical, as they are heavy waste producers.