Plecostomus

These fish are sold when they are young and small, but they can grow to be a maximum size of 50 centimetres (20 in). In the aquarium, this dark-colored, bottom-feeding, nocturnal catfish is often purchased for its ability to clean algae from fish tanks but also contributes a lot of waste to the nitrogen cycle. They are difficult for other fish to harass, both due to the semi-aggressive nature of the fish as well as its thick armor.