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A quick guide to Pleco’s


A quick guide to Pleco’s

A guide to Pleco’s

Pleco’s, or Plecostumus’ are a genus of suckermouth catfish from the family Loricariidea.

For beginner aquarists, Pleco’s can quickly become confusing.  Often when you see one in the pet shop they are small and labelled as ‘Pleco’, which doesn’t tell you a great deal.  There are though, 150 plus species of Pleco, so it’s a good idea to know what you’re buying before you do.  I see issues regularly where someone has purchased a 2 inch Pleco for their small community tank which turns out to be the likes of a common or sailfin and grows into a 2-foot monster.  This is certainly a situation to avoid so I have whipped up this short guide to Pleco’s to give you a helping hand.

Pleco’s are often thought of as algae eaters, but most are omnivorous and will opt to eat fish food over algae, so a Pleco isn’t necessarily going to keep your aquarium algae free.


Commonly available Pleco’s

There are several species of Pleco that you will come across in almost every aquarium shop, so we’ll cover the most common ones here.


  • Bristlenose Pleco:  The Bristlenose Pleco is pretty common, these guys remain relatively small and don’t usually exceed 5 inches in length.  These guys are actually fairly good at cleaning the algae from your aquarium.  But like all Pleco’s they do create a good amount of mess.  So that algae will be converted into Pleco poop to make a mess of your tank instead.  Male Bristlenose get long bristles growing on their face as they mature, females may get one or two short bristles but they are pretty easy to sex.  They will readily breed in the aquarium and will usually select a small cave to breed in.  These guys come in a few colour varieties, but all are the same species.


  • Common Pleco:  The common Pleco is often seen for sale as a small juvenile.  These are the guys often labelled as ‘Pleco’.  The common Pleco will help out with some algae clearing as a juvenile but as it grows into a 2-foot monster fish, it will become territorial and opt for your other fish’ food over the algae.  As juveniles, they are easily confused with Bristlenose, so this is where mistakes can happen.  Once they grow they can be difficult to find a home for, partly due to their size but also due to just how common they are.


  • Sailfin/Leopard Pleco:  The Sailfin is in the same boat as the common Pleco, it gets just as large and is usually sold as a juvenile, which again could be confused with a Bristlenose by a new aquarist, or anyone who is inexperienced with Pleco’s.  These guys do get territorial as they grow.  I rescued one a while ago which was around 12 inches long, at feeding time it would fly around the entire 600-litre aquarium bashing other fish away from the food.  These larger species produce a lot of waste too, so if you’re after a fish that will clean your aquarium up, these guys are not the ones for the job.  It’s probably rarer to see them not pooping than it is to see them squeezing one out, it really is constant.


Sailfin Pleco


These are the three most common, but there are many more that are widely available.  However, if I list them all here, this won’t be a ‘quick guide to Pleco’s’, it will be a really long and drawn out guide to Pleco’s, so if you have questions about a specific species then feel free to ask away in the forums.

Pleco identification

A far too regular occurrence in fish shops, particularly the chain stores, is to come across a fish you like the look of and enquire about it, only to find out that the staff can’t even tell you what it is.  This is how many aquarists end up stuck with a 12-inch Pleco in a 16-inch aquarium.  So, it’d be really handy if we could tell the difference between the smaller species and the monsters.  Luckily for us, there is a way that’s quick, easy, and will hopefully mean you know what you are buying.

If you take a look at the dorsal fin (the one on the fish’ back), you will notice it has a number of rays in it.  They can be quite difficult to count if the fish is small so taking a quick photo will help.  But if there are more than 10 rays in the dorsal fin, then it’s a bigger variety of Pleco and could grow to 24 inches plus.  This is the first step in Pleco identification if the shop staff can’t help.

Other than that it may be a case of doing some research, try to find a Pleco online which matches the pattern of the fish you are looking at.  Once you’ve found that, google the identification given of the Pleco in the photo you have found and see if it matches the rest.  There are millions of articles on fish online, so the chances are that you will find one to have a quick read up before you make a purchase.


Pleco identification



L number Pleco’s

You may have, at some point, heard Pleco’s referred to with L number names.  The L number system is classed as semi-scientific, it started because many species of Pleco were being shipped around the world and couldn’t be identified.  So L numbers were assigned based on photos of the fish that were being shipped.  L numbers are retired once the species has a scientific classification.

L numbers can be confusing as some species have more than one L number, and some L numbers refer to more than one species.  So, if a Pleco has a scientific name, it’s best to use that as its identification.  There are still a lot of L number Pleco’s though which don’t have one yet.

This all makes L number Pleco identification a little hazy, but it can be done, you just need to do a little research.

If you’re interested in taking a look through the full list of L number Pleco’s then here is a link.  This is pretty handy as most of them also have photo’s, but it doesn’t include the alternate L numbers given.  If you’re interested in those then see this link for a full list from www.theaquariumwiki.com.



A word of warning

Some Pleco species, particularly larger more territorial species can do damage to your other aquarium inhabitants.  Pleco’s can get a taste for the slime coat on other fish, and if they do they will try to eat it, which can cause significant damge to the fish it’s got hold of.  Slower moving fish are particularly at risk, Bichirs for example are a common target.

When larger species do go a bit mad, like mine did, they can also cause damage by ramming fish.  A large armoured catfish swimming at speed can be quite the battering ram.  I once saw my Sailfin ram a Jack Dempsey so hard that the poor JD looked like it had a fit.  Luckily JD’s are quite tough and it quickly recovered but I decided to move the Pleco to another tank after that.



Buying a Pleco?

If you’re looking to buy a Pleco for your aquarium, then hopefully this quick guide to Pleco’s has helped a little.  The important things to remember are:

  • Always ID a fish before you buy it.

That’s it, if you have a definite Pleco identification and you know you can take care of it, that’s all you really need.  Pleco’s can be very rewarding to keep and there are some very spectacular species around.


Buying a pleco


Show us your stunning Pleco’s by using #seriouslyfishyclub on your next Instagram photo of them.


About the author

James @Seriously Fishy

I am a fish keeping enthusiast with over 20 years experience. I currently keep American Cichlids (CA) which are my favourite fish to keep so far. I started Seriously Fishy as I noticed a large volume of people on various web pages looking for help with Aquarium basics. I created the first Seriously Fishy book to solve the issue in 28 pages, that led to the Seriously Fishy UK fish forum and blog.

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