Loricariids (from Loricariidae, the taxonomic family to which plecos belong) can appear primitive with their thick armored plating and cling-on lifestyles, but they are actually fairly advanced fishes whose fossil record dates back to only around 23 million years ago. The jaws of plecos are highly advanced and diverse between species, helping to explain why they don't all consume the same types of algae or why some plecos exhibit more vegetarian tendencies than others.

Pleco Anatomy

While body shape and color are extremely variable among Loricariids, the two constants between all members of the family are armor plates and sucker-mouths. Suction is used to stay attached to objects, but plecos actually scrape algae and detritus off instead of vacuuming it up.

Plecos have eye structures called "iris operculums" that can control the amount of light entering the eye and also disguises the eye-spot that might give their camouflaged bodies away. When the operculum is closed the pupil of a pleco resembles the Greek letter omega, so the completely modified iris is called an "omega iris."

Like many organisms, plecos exhibit sexual dimorphism, or a difference in morphology/appearance between male and female. Many plecos actually have teeth on their skin called "odontodes," and in males they are usually very large and more numerous than in females. Some genera like the Ancistrus sp. plecos have more specific sexual dimorphism. In the case of Ancistrus the males tend to have long, fleshy tentacles on their snouts while females have reduced tentacles or none at all.

Pleco Behavior

A majority of pleco species are territorial and nocturnal. A popular aquarium species that serves as an exception is the Otocinclus catfish. Even small or medium-sized plecos tend to reserve entire tanks for themselves in captivity, so aquarists should beware of adding more than one mature pleco. Territorial fights are more likely with increased age and if both of the plecos are of the same sex.

Plecos primarily originate from fast-moving streams and river basins in Costa Rica, Panama, and South America. Rather than attempting to fight the current in those areas, they instead evolved to latch onto the nearest bit of debris and hang on, and many plecos have trouble swimming once mature. Instead they tend to pull themselves along by their sucker-mouths or "scoot" in little spurts of activity along a given surface. This riverine origin should also be noticed by aquarists, as many pleco species enjoy a current in their tank as well as vigorous filtration.

Plecos have variable diets, but are primarily omnivores. Different genera prefer different ratios of vegetation to meat. For example, Ancistrus are mostly herbivorous while Hypancistrus and Baryancistrus are mostly carnivorous.

Like most fish plecos utilize external fertilization when they spawn. It is typically the male of the species that cares for offspring. He will guard the eggs, turn them over with his mouth, and fan them with his pelvic fins to supply oxygen. Plecos spawn in caves surrounded by mild currents. Some species have males that will continue to guard the offspring as fry (baby fish), and pleco parental instinct tends to be well-developed.

What Are L-Numbers?

If you have ever looked up information about plecos before, you may have noticed aquarists classifying their plecos by an L-number, like L025 for the "red-tailed scarlet pleco" (Pseudacanthicus sp.). L-numbers are the invention of the German aquarium magazine "Die Aquarien und Terrarienzeitschrift (DATZ)," and are used in lieu of scientific names for aquarists to identify plecos. Scientific names are the universal names for species, but in the case of Loricariids (that's where the "L" in the L-number comes from) there are so many species that many have not been assigned a name yet.

The L-number system isn't perfect. For example, the English-language books that were published with L-numbers did not always match numbers to species as the DATZ magazine did. Furthermore, different populations of a single species may be given different L-numbers, or whole genera may be given only a single L-number. However, L-numbers are the closest aquarists can get to a scientific/universal taxonomy for the hundreds of pleco species.

Warning!

The term "algae eater" isn't really the best one for plecos. Better common names would be "#1 handsome fish" or "grows-to-over-a-foot-long fish." Unfortunately plecos don't all eat the same kinds of algae, and many of them won't even touch the algae in your tank. Thinking that a fish will handle your algae problem for you (and that you don't have to feed it anything else) leads to a lot of plecos starving or outgrowing their tanks. Never buy a small common pleco for your algae problems, and do your research before you buy a difficult or sensitive species.

Even though the common plecostomus (Hypostomus plecostomus) isn't a good choice for most aquarium owners, there are hundreds of pleco species in all different sizes, shapes, and colors! It's a matter of matching your tank and skill level to a species rather than choosing to pleco or not to pleco.

Here are some aquarium parameters you should consider in choosing the right pleco for you:

Aquarium size. I used to work at a pet store in high school, and 10-gallon tanks were easily the most popular sellers. They're cheap and can house a lot of different types of animals. However, you don't want to buy a common plecostomus that grows to over a foot in length for that tank! Good Loricariids for a small tank include Otocinclus catfish (2"), clown plecos (4"), or bristlenose plecos (3"-5").

Maintenance. Do you have a large tank but tend to neglect your regular water changes? Many attractive plecos like the royal pleco grow large (in the royal's case to about 17") and produce a huge amount of waste. Plecos themselves are generally hardy and can tolerate very dirty water, but your other fish are likely to be less healthy when forced to live alongside their grungy neighbor.







pH of Your water. pH is a measurement of water acidity/alkalinity, and different fish have evolved to live in different pH levels. While many plecostomus are hardy and can tolerate significant pH changes, you should not leap into buying a rare species without checking its pH requirements first. 0 on the pH scale is the most acidic, while 14 is the most alkaline. Completely pure water would have a pH of 7.0, but most of us using tap water are going to have variations from that number (usually toward the "hard" or alkaline end, which is the opposite of a typical pleco's natural environment).

To find out the pH of your tap water, pour some into a bucket, leave it overnight, then run a pH test using an aquarium testing kit. Water fresh from the tap is not "settled" the way it would be in your aquarium. For most plecos, your only goal is to provide a stable pH rather than reaching a specific pH value.

Here is a list of some common plecos in order of increasing size:

Otocinclus sp. (otos, otocinclus cats) - 2"
[albino] Ancistrus sp. (albino bristlenose pleco) - 3"
Hypancistrus zebra (zebra pleco, imperial pleco) - 3"
Chaetostoma milesi (rubberlip pleco, bulldog pleco) - 3" to 4"
[L260] Hypancistrus sp. (Queen Arabesque pleco) - 3.5"
Panaque maccus (clown pleco, ringlet pleco) - 4"
Ancistrus sp. (bristlenose pleco, bushynose pleco) - 4" to 5"
Panaque sp. "peckoltia" (tiger pleco, gypsy king tiger pleco, clown pleco) - 6"
[L142] Baryancistrus sp. (snowball pleco, big white spot pleco) - 10" to 12"
Leporacanthicus galaxias (galaxy pleco) - 10" to 12"
Scobinancistrus aureatus (sunshine pleco, goldie pleco) - 10" to 12"
[L18] Baryancistrus sp. (golden nugget pleco) - 14"
Panaque nigrolineatus (gold line royal pleco) - 15" to 18"
Hypostomus plecostomus (common pleco, plecostomus, algae eater, algae sucker, janitor fish) - 18"

Buying your pleco. When you get to the pet store, examine all the tanks before zooming toward the nearest beautiful catfish. Are there a large number of dead fish in the tanks? Are there sick fish still on display/being sold? Sick fish can be identified by the presence of external parasites such as ich (white dots on the surface of the fish), fin rot (degraded fins with a white edge), open wounds, excessive thinness, or erratic behavior (ex. swimming in a continuous circle or bumping into objects).

Is there overcrowding? See if you can spot a series of pipes connecting all the tanks: if you see pipes, all of the water is being exchanged through all of the tanks. That means if there is ich in one tank, it may be passed on to the other tanks. Ask the clerk if any filters or screens are being used. Unfortunately using a water system that exchanges water between every single tank is the only affordable way many pet stores can maintain a freshwater fish section.

If you don't see too many problems, take a look at the pleco you want to buy. Try to pick out a pleco that is actively swimming about and cleaning off objects. Since most pet store specimens are young, they should be quite active even during daylight hours. At the very least the pleco should try to swim/move away if it is disturbed (ask the clerk to use a bag or net handle to agitate the fish).

Your pleco should have clear, non-cloudy eyes and no wounds or rotting fins. Some fin breakage may have occurred from handling or depending on what fish the pleco was kept with. Be aware that many plecos are spiny and have a defense mechanism of erecting their fore (front) fins, which may or may not have spikes on the end. Aside from being a safety hazard, this means they can get caught up in nets or poke holes in bags. Ask for at least a double-bag and newspaper for your pleco, and check to see if you can be indulged with a triple-bag if it is a medium or large-size fish.

Acclimating your pleco. When you get your pleco home, float the bag in your aquarium for about 10 minutes. Move the bag to a bucket or other container and poke a decent-sized hole in the top. Using a paper cup (or a designated aquarium cup), scoop a little water out of your tank and add it to the pleco's bag once every 5 minutes for 20 minutes. You want to avoid getting too much of the pet store's water mixed in with your aquarium water, so when the 20 minutes is up gently pour out the water from your pleco's bag and move the fish either with another bag wrapped around your hand or with a container. Try to avoid nets, which plecos can get stuck in. Gently release the pleco into the aquarium and keep the lights dimmed with little to no activity around the tank until the next day.

I highly recommend using a small quarantine aquarium for at least a month before you move your pleco into your main tank.

Feeding your pleco. Plecos are called "janitor fish" because most species generally have the refuse that other organisms leave behind as their diet. You should however be supplementing your pleco's diet with quality foods like sliced cucumber, zucchini, or melon. You can weigh down a slice of cucumber with a rock or a vegetable clip. Commercial algae tablets and shrimp pellets (alternated, especially for older plecos) also work, but make sure you add them at night so the pleco can find them before your other fish.

Plecos will eat pretty much anything that can fit in their mouths (including your small fish), so it's up to you to give them the right foods to bump into. Most species will feed off driftwood or from algae that lives on driftwood and many require it for a healthy life. When choosing commercial fish foods, take a look at the listed ingredients. If you see "fish meal" or "processed meal," that food is going to be junkier and less nutritious than one that lists "whole salmon." I prefer frozen foods (ex. worms-- pet stores will carry them) for the meat requirements of plecos, and home-cut vegetables for their vegetarian side.

How often should you feed your pleco? Keep in mind that they are grazers ("cows of the aquarium"), and watch the parameters of your tank when you first start maintaining a pleco in it. Very large plecos may only have to be supplemented once or twice a week depending on the water temperature and season, but small species and smaller specimens of large species (say anything under 5") can be supplemented once a day or once every other day.

One of the most interesting behaviors of plecos can occur at feeding time. Some plecos will swim upside-down to feed from the surface at hours they would normally be inactive, and you can also handfeed these individuals and reduce the need for watching the tank to make sure they get what they need. If your plecos figure out this trick, congratulations! Your feeding regimen just got a whole lot easier. =)

The following is a gallery of a few notable algae eaters. I hope you enjoy the diversity and color of these bodacious cats. =)

• Plecos in the Panaque genus practice xylophagy, the eating of wood. They are one of the few groups of animals that do so.


• Plecos have taste buds over almost their entire body and fins.


• Many plecos can breathe air, including the popular otocinclus cats. The likelihood of a pleco species having this capability depends on whether or not it originates in a low-oxygen environment.


• Aquarists often refer to plecos as "pl*cos" on forums and newsgroups. This is because once upon a time an aquarist was discussing his pet pleco on a newsgroup and the fish immediately died, so the word has been interpreted as bad luck.