Oto catfish are small, algae-eating armored catfish from the genus Otocinclus. The most common type sold in pet stores is the species Otocinclus macrospilus, though 17 species exist in total. They are native to South America and caught wild in southeastern Brazil and Peru.
Otos are easy to keep for the beginner aquarist and are an ideal substitute algae eater for small tanks, because they eat algae similar to Plecostomus catfish but do not grow as large. In addition to the algae in the tank, otos should have access to sinking algae wafers or other vegetable matter on a daily basis.