Plecostomus, pleco, algae eater, or algae sucker, is a general name for a type of freshwater tropical Central and South American fish belonging to the family Loricariidae. Algae eaters are extremely popular in aquaria for their ability to clean tanks by eating algae growth. These fish are typically sold at about 8 cm (3 inches) and may grow up to 60 cm (2 feet), and a few species can reach even more. A relatively new species is hardy and grows to a maximum of 10 cm (4 inches), an ideal size for small to average size tanks.

Plecos are omnivorous but, in the wild, feed mostly on plant material at night. During the day, their unusual omega irises block a lot of the light out of their eyes. The iris opens at night. They can also wink by rolling the eye into the head.

As they age, their foreheads enlarge in a peculiar manner. Plecos can become more territorial and are best kept individually in tanks. Because of their large size and territorial behaviour, when stocking smaller aquaria it is often better to consider a bristlenose catfish (Ancistrus), which generally grow to about 15 cm (6 inches), are very peaceable, and also eat algae. In a suitably large tank a solitary plecostomus will live amicably enough in a community tank alongside other tropical fish. These catfish can be kept in tanks with "cold-water" species like goldfish, Carassius auratus, these tanks need to be heated however.

There are a number of species that are sold on the market under the name common algae sucker, including Hypostomus plecostomus, Hypostomus punctatus, Pterygoplichthys multiradiatus, and Pterygoplichthys pardalis