Hypostomus Plecostomus: Size, Care and Pleco Problems

Hypostomus plecostomus is an armoured, sucker-mouthed catfish from northeastern South America, the fish that gave aquarium 'plecos' their name. Wikipedia describes it as a nocturnal bottom-feeder with a sucker-like mouth and rows of bony plates along the upper body, and notes that it can breathe air: the less oxygen in the water, the more often it rises to gulp at the surface.

There is a naming problem worth knowing. Wikipedia says many fish sold as Hypostomus plecostomus actually belong to a different genus, Pterygoplichthys, the sailfin plecos. The Florida Fish and Wildlife Conservation Commission gives a quick way to tell them apart:

• Sailfin pleco (Pterygoplichthys): a tall dorsal fin with 10 or more rays and a worm-like pattern of dark markings on the head
• Suckermouth catfish (Hypostomus): fewer dorsal fin rays and black spots rather than worm-like lines

Count the rays on a clear photo of the raised dorsal fin; the FishLens app can also identify the fish from a side-on picture.

Up to 50 cm (19.7 in) in standard length, which does not include the tail (Wikipedia). Swell UK warns that common plecos can reach 18 inches in a short time, and Florida's FWC reports feral sailfin plecos over 20 inches and 3 pounds.

That is why the tiny pleco sold as an algae eater for a small tank is a problem. Science Gal Aquatics puts the tank needs of the large pleco types at 100 gallons or more, while smaller species such as the bristlenose stay around 3 to 4 inches and can live in about 20 gallons. If you want a pleco for a normal community tank, a bristlenose is the realistic choice.

Plecos are omnivores. Wikipedia lists algae, aquatic plants, small crustaceans and snails in the wild diet, and Science Gal Aquatics says plainly not to rely on algae alone. Useful foods it lists include vegetable wafers, shrimp pellets, frozen bloodworms and wood-based pellets. Swell UK adds that plecos need sinking food made for sucker-mouthed catfish.

Three other care points from Science Gal Aquatics:

• Driftwood adds fibre to the diet and is essential for some species, such as bristlenose and clown plecos
• Lights off: plecos are nocturnal, so feed after dark and give them a dim period
• Heavy waste: plecos eat a lot and produce a large bioload, so filtration has to match the fish's adult size

A pleco that attacks other fish is usually rasping off their protective slime coat, most often because it is hungry. Hobbyists on the MonsterFishKeepers forum describe plecos that are not fed seeking food from other fish instead, and one keeper reported a pleco that stripped the slime from a bichir until it died. The slime coat is the fish's first defence against infection: Wikipedia explains it traps and sheds microbes and contains antimicrobial substances, so a fish that loses it is open to bacterial and fungal disease.

Slow fish and fish that rest at night are the usual victims. What to do:

• Feed the pleco deliberately, after lights out, with sinking wafers and vegetables such as blanched zucchini or cucumber (MonsterFishKeepers; Science Gal Aquatics)
• Add driftwood for species that rasp wood (Science Gal Aquatics)
• Separate the pleco if attacks continue, and move injured fish to a hospital tank
• Check the size match: a large pleco in a small tank with slow fish is the riskiest combination

If an injured fish develops fuzzy patches or red sores, ask an aquatic vet or an experienced fish shop for treatment advice.

Not if they get space and food; Wikipedia gives 10 to 15 years in captivity. The common failures are the ones above: a fish bought for a small tank that outgrows it, and a fish left to live on algae until it starves or starts rasping other fish. Science Gal Aquatics gives water of 72 to 80 F and pH 6.0 to 8.0 for plecos in general, and Wikipedia 22 to 30 C and pH 6.5 to 7.5 for this species. Choose the species by adult size first, then set up the tank for it.

Armoured catfish are eaten in some places, but check the species and the water first. Florida's FWC rates the edibility of feral sailfin catfish as fair to good, notes they are hard to clean and best cooked whole, and sets no bag or size limits because they are non-native. Fish from polluted or urban water can carry contaminants, so follow your local fish consumption advisories, and do not eat an aquarium fish that has been given medication.

The bigger issue is escape. Wikipedia lists established non-native populations in Bangladesh, India, Malaysia, Indonesia, Sri Lanka, the Philippines, Taiwan and parts of the United States, and FWC reports that sailfin plecos dig spawning burrows that can undermine canal banks and lake shores. Never release a pleco; rehome it through a shop or club.