Fish

Plecostomus

Hypostomus and relatives · also called pleco, plecostomus, suckermouth catfish, janitor fish

Least Concern → omnivoreherbivore Rainforest Rivers & wetlands

A plecostomus is the fish sold to eat your algae — a flat, armoured, sucker-mouthed catfish clamped to the aquarium glass. The problem is that the two-centimetre fish in the bag becomes a half-metre animal in a few years, one of the messiest in the hobby, and when frustrated owners tip it into a warm river it digs into the banks and takes over.

Overview

Plecos are armoured catfish (family Loricariidae) from South America, covered in rows of bony plates with a sucker mouth ringed by a fleshy disc that lets them clamp onto rock and glass. They rasp algae, biofilm, and wood fibre with fine teeth. Most are nocturnal and need a cave or log to hide in by day.

More than a janitor

Sold as clean-up crew, a grown pleco actually needs vegetables and driftwood, not just algae, produces heaps of waste, damages plants, and reaches 30–50 cm in a few years — far too big for a typical tank. This is why so many are abandoned. Smaller bristlenose plecos (10–15 cm) are the sensible alternative.

Invasive burrower

Released Pterygoplichthys plecos can gulp air and survive foul water, and have colonised warm rivers and canals in Florida, Texas, Hawaii, Mexico, and tropical Asia. Females dig metre-long nest burrows into banks; colonies of them accelerate erosion and collapse. The armoured adults foul nets and have almost no predators.

Status

Least Concern for the common farmed species. But prized rapids-dwelling plecos like the zebra pleco of the Rio Xingu are Endangered or Critically Endangered, hit by dams and heavy collection.

Plecostomus: common questions

Are plecos good algae-eaters for a beginner tank?

Only with big reservations. A small pleco does graze algae, but it grows quickly to 30 centimetres or more, becomes one of the messiest fish in the hobby, needs driftwood and vegetable food rather than living on algae, and often damages soft plants. For a standard community tank, smaller and more manageable algae-eaters, such as certain small bristlenose plecos, otocinclus catfish, shrimp, or snails, do the job without outgrowing the tank. The common pleco really suits only a very large aquarium set up with its needs in mind.

How big do plecos get, and how long do they live?

The common pleco reaches about 30 to 50 centimetres depending on species and conditions, usually within three to five years, and a healthy one can live 10 to 20 years, sometimes longer. This mismatch between the tiny fish in the shop and the large, long-lived animal it becomes is the central problem with the species. Bristlenose plecos stay much smaller, around 10 to 15 centimetres, and are the better choice for anyone without a very large tank.

Why are released plecos such a problem?

Plecos dumped by aquarists have established in warm waters in Florida, Texas, Mexico, Hawaii, and across tropical Asia, and they cause several kinds of harm. Females excavate metre-long burrows into riverbanks and canal walls to nest, and dense colonies of these burrows speed up erosion and cause banks to collapse. The heavily armoured adults have few effective predators, they compete with native fish for food and space, and they foul and damage fishing nets. Their ability to breathe air and survive terrible water quality lets them thrive where native fish struggle.

What do plecos need in an aquarium?

A pleco needs a tank matched to its adult size, which for a common pleco means several hundred litres, strong filtration and frequent water changes to cope with the waste, at least one cave or hollow log to hide in by day, and a piece of real driftwood, which many species must rasp on for fibre and to aid digestion. The diet should be mostly vegetable, such as blanched courgette, cucumber, and spinach, sinking algae wafers, and vegetable pellets, with only occasional protein foods. Water should be warm, well oxygenated, and clean.

Sources & further reading

Written by HideShark Editorial Team · reviewed by HideShark Science Desk. Published September 11, 2026. Last updated September 11, 2026.

Quick facts

Scientific name: Hypostomus and relatives
Diet: Largely a grazer, rasping algae, biofilm, and the layer of decaying plant and organic matter from rocks, wood, and the bottom with a mouth full of fine teeth, along with soft plant material and wood fibre, which several species deliberately gnaw and can partly digest, plus some worms and insect larvae
Armour and a sucker: A pleco is covered in rows of overlapping bony plates instead of scales, has stiff spines in its fins, and has a large downturned mouth ringed by a fleshy disc that works as a sucker, letting it clamp onto rocks and glass in current and hold position while it grazes
Not just an algae-eater: Plecos are sold as clean-up fish, but a grown pleco eats far more than algae, needs a substantial share of vegetable and, for many species, wood in its diet, produces a large amount of waste, and often ignores the algae on the glass while rasping holes in aquarium plants, so it is a poor match for a small planted tank
It outgrows the tank: The common pleco, usually a Hypostomus or Pterygoplichthys species, is sold at a few centimetres long but reaches 30 to 50 cm in a few years, far too big for the tanks most buyers have, which is why so many are abandoned, given away, or released
Breathing air: Pterygoplichthys plecos can gulp air at the surface and absorb oxygen through a modified, highly vascular stomach, which lets them survive in warm, stagnant, low-oxygen water, endure being out of water for many hours, and travel short distances over land, all of which help them as invaders
Invasive burrowers: Released plecos, mostly Pterygoplichthys, have established in warm rivers and canals in Florida, Texas, Hawaii, Mexico, and much of tropical Asia, where the females dig long nesting burrows into the banks that accelerate erosion and bank collapse, and the armoured fish clog nets and are largely inedible to native predators
Nocturnal and shy: In the wild and the aquarium a pleco spends the day wedged under wood, rock, or an overhang and does most of its feeding and moving at night, and many species need a cave or hollow log to feel secure or they become stressed
Range: Native to fresh waters across tropical and subtropical South America and into Panama and Costa Rica, in rivers, streams, floodplain lakes, and swamps from clear rocky rapids to muddy, slow, oxygen-poor backwaters, and introduced and established in warm rivers, canals, springs, and reservoirs in the southern United States, Mexico, Puerto Rico, Hawaii, and much of South and Southeast Asia.
Conservation status: Least Concern → ≈ The common aquarium plecos belong to species that are widespread in South America and assessed as Least Concern, and they are farmed in huge numbers for the trade, while some released populations are now damaging invasive species in warm regions worldwide. Within the armoured catfish family, however, many species are highly restricted, and a number of prized aquarium plecos, especially the zebra pleco and other Hypancistrus and related species from single stretches of Brazilian rivers such as the Rio Xingu, are Endangered or Critically Endangered, threatened by hydroelectric dams that have flooded or drained their rapids habitat and by heavy collection for the ornamental trade in the wild