The Giant Plecos

Author: Bob Fenner

Plecos are the go-to algae eaters for many hobbyists, but some species require huge setups to thrive. An expert hobbyist discusses these large catfish and provides excellent care advice so they can live in your tank for years to come.

Great Little Suckers

The South (and some Central) American family Loricariidae, the suckermouth catfishes, has something for most all freshwater aquariums. Otocinclus and similarly small sized Parotocinclus and Hypoptopoma genera (the family consists of 92 genera) can be kept in 10-gallon or larger systems in small shoals, while some of the monsters we’ll cover here require hundreds of gallons of space, not to mention considerable circulation and filtration, to keep their systems clean.

Identification and Range

Members of this family of armored catfishes are easily recognized by the subterminal (bottom) orientation of their mouths and locomotory mouth process. Some plecos live at elevations of more than 3,000 meters (more than 9,800 feet), moving up steep rocks and waterfalls by shifting their bodies and mouths. There are some 800 described species with speculations that there may be 1,200 to 1,500 total. Plecos and kin can be found in Central America (Costa Rica, Panama on down) and throughout South America in nearly every body of fresh water. There are no marine or brackish species; so no, they don’t like salt in their water.

Common names and scientific ones abound for these catfishes, and you are encouraged to seek out modern references, like the site for good image work, and for meristics and morphometric data per species.

Hypostomus plecostomus, otherwise known as “the original pleco,” is often touted for smaller systems, though it is not suitable for them. This erstwhile workhorse is also a “monster plec,” with most topping out at a foot in lengthbut capable of reaching nearly twice this dimension.

Genus Pterygoplichthys

Two species of rather larger "plecostomus" are bred and reared in large quantities for the aquarium trade, using pond techniques perfected at farms in Florida. Liposarcus anisitsi (Eigenmann & Kennedy 1903) is the snow king pleco (formerly of the genus Pterygoplichthys) and grows to 17 inches in length (30 inches according to Burgess 1989). The leopard pleco (Glyptoperichthys gibbiceps, Kner 1854), formerly Pterygoplichthys gibbiceps, reaches about 20 inches maximum.

There are a few other species that make their way into the trade, like P. multiradiatus, the Orinoco sailfin plec, and P. scrophus, one of the plecs called “rhino,” though these are rare.

Behavior Notes

Giant plecos, like their more diminutive brethren, are principally nocturnal, eschewing the daylight to move about, seeking food in the darkness of night. Though you may see them out and about during light hours, this is not their preferred time, and this behavior may well indicate that there’s insufficient fodder (so place some food during lights out for them), something is amiss with water quality, or their tankmates are bothering them.

One other aspect of behavior that should be noted is these fishes’ prodigious production of waste. Likened to sea cows, they take in a good deal of food volume, and it all ends back up in their system. Hence their need for large tanks, with plenty of water movement, mechanical filtration, and regular (weekly) gravel vacuuming and water changes to maintain decent water quality.


Like most armored catfishes, few fishes will bother to tackle their tough sides, but the opposite isn’t always so. The instances of rogue behavior, of these fishes sucking on the sides of easygoing (e.g. goldfish) to more rambunctious (large cichlids) tankmates is quite common and something you should be on the lookout for, possibly calling for the physical removal or separation of parties involved.

These loricariids can be feisty with others of their family and, at times, conspecifics (members of the same species). If there’s room, and in particular if they grow up together, this may not become so much of an issue for the latter, but again, the onus is upon you to assure that all are getting along.

Though these larger suckermouth cats are not plant eaters per se, they will definitely damage soft-leaved to waxy plants even if there’s enough food and greenery around.

Stocking and Selection

Picking out a good specimen of these fishes is generally straightforward. One item that needs to be stated and reinforced is to not buy newly arrived specimens, for a few reasons. Because of the trauma of collection (whether cultured or not), shipping, and placement in very different environmental conditions, and the mal-effects of starvation ahead of transport, there are times when massive mortalities of these species occur—almost always within a few days of getting to a dealer’s tank.

Wait a handful of days or pick out yours from stock that has been around a while. And do assess whether the individual’s stomach is hollow or full. You don’t want ones that are too thin, and it’s very hard to tell how well-fleshed they are by examining any other part of the body. Use a net to nudge the fish up on the side panel of the tank to look at its belly. Healthy specimens have convex undersides and bulging eyes. Poor ones have concave undersides and sunken eyes.

A note regarding de-selection of these fishes due to their prodigious adult size: Quite often, otherwise well-meaning aquarists will end up with giant plecos that are too big to do well in their limited-size aquariums. Don’t despair, but do be aware, pro-active, and humane in getting them to suitable environments. Often, fish stores will trade you a smaller specimen (or two!) for your too-large pleco. Barring this avenue, aquarium service companies often have need and room for large plecos. You can usually locate these businesses via the internet or other business directories.

Large Pleco Systems

There are three main requirements for large pleco systems: They must be big, well-filtered, and established. They are or become very large animals in short time with good care, and are amazingly messy in their food, waste, and burrowing habits. Even small individuals should be kept in nothing smaller than 20 gallons, and larger ones require at least 150.


These suckermouth cats live in relatively clean, fast moving, mostly riverine conditions. Hence your water movement and mechanical filtration should collectively provide a good ten turnovers of water per hour. And even with all this volume to dilute wastes, gear to move and filter water, considerable (20 to 25 percent) weekly water changes, incorporating thorough gravel-vacuuming in the process, are strongly encouraged.


Though largely sedentary, the large plecos need high levels of dissolved oxygen; the more aeration the better. Folks often observe them going to the water/air surface and taking in and exhaling breaths. This may be an indication of too-low available oxygen or poor conditions (nutrient accumulation especially).

The note regarding placing these fishes only in well-cycled systems should be revisited. Do not place plecos of any kind in new systems. The water quality is not to their liking, nor are the vicissitudes of being exposed to metabolite accumulation ahead of cycling. Additionally, as you can appreciate, there is little for them to feed on when the tank is new.

Water Requirements

Water-quality wise, these fishes enjoy a wide enough tolerance of pH (6 to 8 is fine), water of medium to moderate hardness, and tropical temperatures (mid 70s to lower 80s F). Regular dechloraminated tap water is good for them in almost all cases.

Lastly, I’d like to mention that these fishes need to be protected from being burned by heaters. These should be fitted with commercial or do-it-yourself covers to prevent such injuries.


Many people misunderstand these plecos’ dietary needs. One, they are not “cleaner uppers” of fish feces, nor will they live long or well on leftover foods you’ve presented to your other livestock. In the wild, these fishes feed throughout the night on plant and animal materials and sunken driftwood. For yours to do well, it needs to be offered these types of foods during lights-out hours. Bogwood must be present in the systems for dÉcor, hiding places, and dietary fiber.

Plant materials that have been employed to good use include types of eggplant, squash, sweet potato, and carrots. These are best par-boiled or moderately microwaved to make them more chewable. There are several excellent tablet foods that incorporate meaty and vegetable matter as well—and these can be applied profitably if you can get them past more active feeders. This usually does not prove to be problematic if you develop and adhere to a program of offering food about the same time (lights out) and place.


By and large, these are tough aquarium species, usually showing signs of parasitic and infectious disease later than other fishes in the same system. Almost all of these large species are farm-bred and raised, hence the usual troubles affecting wild-caught specimens, Epistylis, gill flukes et al, are a rarity. Most often, the cause of premature death is environmental stress—the result of being kept in too-small aquariums. Lack of nutrition is the next likely cause.

Correcting water quality and other system issues is almost always efficacious to solving health issues, and parasitic ones can be easily cured with commercial treatments and/or thermal manipulation (e.g., raising temperature for ich).

Unless your water is very soft, medications are well-tolerated at full doses, with one notable exception: the use of salt. These are not brackish-water animals, and they will tolerate only about a teaspoon of salt per five gallons. Most freshwater sources already have some salt in them. So, if you’re keeping organisms that prefer salty conditions (e.g., many molly species), then tankmates other than plecos are desirable.


As previously alluded to, these pleco species are captive produced, usually in mud ponds, in which males dig tight-fitting burrows into the sides, attract females, and use their bodies to block the entrance while incubating eggs and fry. If you have a system of a few hundred gallons, you might try supplying yours with a sunken pipe with one end open.

Consider Carefully

Way too often abused out of lack of knowledge and understanding, the larger species of plecos need space, delivered foods, and a modicum of regular maintenance to do well in captivity. If you think about their natural environments, capacity for growth, and ultimate size, it will make sense to select smaller species from the get-go if you don’t have the capacity or intention of providing for their adequate care. There are literally hundreds of other loricariid species, bushynoses (Ancistrus), clown plecos (Peckoltia), and more, that go well with other tropicals and stay small enough for hobbyist systems. What is more, several of the latter are more attractive than the giant plecs and more interesting behaviorally.