Opisthoproctidae is a family of fish commonly known as the "upside-down catfish." These freshwater fish are primarily found in the rivers and streams of South America. They are characterized by their unique swimming behavior, often swimming upside down, which helps them feed on algae and detritus on the water's surface. Members of the Opisthoproctidae family have flattened bodies and large, protruding eyes, which aid in their unusual orientation. They typically inhabit slow-moving waters and are known for their peaceful nature, making them popular in aquariums. Their distinctive appearance and behavior make them a fascinating subject of study in aquatic biology.