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Are Plecos Aggressive?

Plecostomus (or ‘plecos’ as they’re often called) are big, omnivorous fish and well-known in the aquarium hobbyist world. Found in the rivers of the Amazon jungle in South America, these scavengers like to eat algae, plants, and any dead fish they can find! They’ll often attach themselves to hard surfaces or other fish, especially in a freshwater tank. But are they aggressive when in captivity?

Most plecos have a peaceful temperament and usually get along well with other fish when kept in a large, well-maintained tank. If underfed or overcrowded, they can become aggressive. As well, plecos will fight to the death to defend not only their territory, but their offspring. Plecos don’t like to be kept together and often become hostile towards other of their kind in a captive environment.

Now that you know plecos tend to be peaceful in nature, let’s examine this topic further and in more detail. Together we’ll learn which types are the most aggressive, whether (or not) you can keep them in the same tank together, if they bite one another, what to feed them to reduce hostility, and which fish make the best tankmates.

So, if you’re ready to learn more about plecos are their behavior/disposition in captive aquatic environment, the let’s begin!

What is the Most Aggressive Pleco?

Leopard frog (also called imperial tiger) plecos are known to get aggressive, especially when their claimed territory is invaded. In fact, males of this species will often fight each other for space in a tank that’s too small or devoid of hiding places. Females, on the other hand, will become extremely hostile and attack any predatory fish to protect her eggs and/or fry.

Honeycomb (or LO37) plecos also tend to be aggressive and may chase after or harass other plecos, especially the larger ones. There are even reports of royal plecos trying to jab the hands of their owners when they reach in to clean it! In short, if almost any pleco feels its territory is being invaded, it’ll become hostile, regardless of size.

What is the Most Peaceful Pleco?

Almost all species of pleco fish are peaceful it they’re healthy, well fed, and have plenty of space to claim their own territory. Bristlenose plecos, for example, are very popular and said to be mainly docile by aquarium hobbyists. Other smaller species like gold spot, rubber lip, zebra, and clown plecos are also reported as calm and gentle in a community tank environment.

In general, plecos as a species – regardless of size or type – are peaceful, under the right aquatic circumstances, that is. If kept alone in a big enough tank with other docile fish, you’ll likely have no problems. However, if you house them with others of their kind, they’ll get territorial and aggressive. This species, contrary to what you’ve learned about most aquarium fish, does best on its own.

leopard sailfin pleco

What Fish Can You Put with a Pleco?

Since plecos tend to be mainly peaceful in a community tank environment, you can keep them with a variety of fish – provided they’re not too large or overly aggressive, that is. As bottom-dwellers, plecos prefer to dwell near the substrate so any fish that likes to swim in the middle or near the surface is a good choice.

Depending on the size of your tank, you can house plecos with a variety of fish including angels, bettas, barbs, cories, gouramis, guppies, mollies, platies, swordtails, bala sharks and tetras. Please note that not all 10 of these fish can necessarily be kept together themselves, so you must research their temperaments and learn what specific water conditions each species requires beforehand.

Can a Pleco Bite?

While plecos do indeed have teeth, it’s very rare that they’ll bite. The only time they may become aggressive and lash out is if other plecos attempt to invade their aquatic space. Highly territorial in nature, they’ll chase and nip at other fish they deem as threats, especially during the mating season when their instinct to protect their offspring is in high gear!

Do Plecos Like to be Kept Together?

In general, plecos don’t like to be kept with others of their kind. One male and one female in a tank for breeding purposes is really the only time you should house them together. While still young, multiple plecos are usually ok in the same aquarium but as they age, they’ll tolerate each other less and less with the males often fighting each other for territory and dominance.

Can 2 Plecos Live in the Same Tank?

I wouldn’t recommend any more than a single pleco in a tank at any given time. Though peaceful and friendly towards other species of aquarium fish, they don’t like to be kept together. Highly territorial, especially when in captivity, they’ll often harass each other – chasing about and nipping at one another. For this reason, having an extra-large planted tank with plenty of hiding places is recommended.

How do I Know if My Pleco is Hungry?

When plecos are hungry or underfed, they may become more hostile. Their innate desire to compete for food will cause them stress, often resulting in heightened aggression. Should you notice your pleco chasing after others at feeding time, you may need to provide them with more food more often. If properly and sufficiently fed, plecos are usually peaceful towards other fish in a community tank.

How do I Know if My Pleco is Stressed?

When a pleco is anxious or stressed, it’ll often become more aggressive. Typical signs of anxiety include erratic behavior such as frantic swimming, crashing into the aquarium glass, lying motionless along the substrate, not eating, constantly rubbing along rocks or other decorations, and chasing after or nipping at other tankmates.

How do I Know if My Pleco is Sick?

If a pleco is sick, it may become more hostile and suddenly lash out at its fellow tankmates when it never used to before. The typical symptoms of disease, however, are lethargy and the refusing to eat. As well, look for bloating and loss of coloration. Fin rot is common in bottom-dwelling fish like plecos and should be treated immediately with antibiotic medication.

Will Plecos Suck on Other Fish?

Plecos have a peculiar tendency to ‘suck on’ or attach themselves not only to hard surfaces but to other fish as well – especially those that are large and slow-moving. This behavior, though not necessarily considered to be hostile, can be problematic for whatever fish it latches on to. It can lead to open sores which then become prone to disease and/or bacterial infection.

Will Plecos Attack Each Other?

Male plecos have been known to bully and attack each other when housed in the same captive aquatic environment. Two females may be able to coexist in the same tank, but it must be very large with plenty of hiding places. For the safety of pleco fish and their fellow tankmates, it’s recommended you keep just one at a time.


In summation, plecos are generally friendly and peaceful towards tankmates in captivity. The only times they become anxious and/or hostile is when their territory is being invaded or they’re competing for food. For these reasons, it’s imperative they be fed well and kept in a large aquarium with plenty of space and hiding places.

I trust this article has been both interesting and informative regarding pleco fish and their temperament in captivity. Thanks for reading and good luck with your aquarium hobby.

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