Pleco Coming To The Surface, Gulping For Air

Plecos gulping at the surface, why do they do it? Find out below.

“Plecos” is a common name for species belonging to the Loricariidae. If you’ve ever kept a pleco, any species of pleco, you’ve likely noticed the fish dashing to the surface. You might wonder, what is the pleco doing and why.

Plecos Gulp At The Surface For Two Reasons

Plecos gulp for air at the water’s surface for two reasons. First of all, plecos will gulp at the surface if they are in a low oxygen environment, i.e. if the dissolved oxygen levels in the water are low. Also, plecos will sometimes take air from the surface if they are suffering from buoyancy issues.

Low Oxygen Levels Can Cause Plecos To Gulp Air At The Surface

If you’ve ever had an air pump break on any of your aquariums, then you know what the result is: your fish will be gulping for air at the surface of the water. This is because gaseous exchange cannot occur without agitation of the water’s surface. Oxygen, a gas in the air, is best absorbed into your aquarium’s water when the surface is disturbed (i.e. there is a lot of splashing). An airstone, or a filter’s outlet, can often agitate the surface enough to keep your water sufficiently oxygenated.

bristlenose plecos are known for gulping at the surface in low oxygen environments

When it comes to plecos, especially some of the smaller species, they inhabit very fast flowing water in the wild. Fast flowing water is very well-oxygenated because the surface of the water is turbulent. Therefore, some plecos can have a higher dissolved oxygen requirement than fish from slower moving water.

So, your first step if your pleco is gulping will be to add another air pump and airstone to see if that resolves the issue. This is especially important if your pleco swims to the surface for air on a regular basis. Conversely, if the behavior is something you only observe intermittently then low dissolved oxygen is less likely to be the cause.

What Causes Low Oxygen In Aquariums?

A lot of things can cause low oxygen in your aquarium.

First of all, a lack of surface agitation is the main cause of low dissolved oxygen in your aquarium. When the water’s surface is turbulent, it allows for much improved gaseous exchange. What does this mean? Well, the air contains oxygen, and for that oxygen to enter the water readily, the water must be moving and splashing at the surface. This is why fast flowing streams are well-oxygenated, whereas stagnant ponds are not.

The next prime culprit for low oxygen is an overstocked aquarium. More fish equals more respiration, i.e. the more fish there are and the bigger those fish are, then the more oxygen they’re taking out of the water.

Temperature is next on the list. This is because warmer water holds less oxygen than cooler water. So, if you are having issues with your fish gulping at the surface, then you should consider lowering the temperature in your aquarium while maintaining a warmth suitable for your fish.

The last major cause of low dissolved oxygen in your aquarium is decaying matter. It’s not the matter itself that consumes the oxygen, but rather the aerobic bacteria feeding on that matter. So, another solution to low dissolved oxygen is to perform larger and/or more regular water changes at the same time as removing excess detritus.

Buoyancy Issues Can Cause Plecos To Gulp Air At The Surface

If your pleco only dashes to the surface once in a while, then it probably isn’t caused by a low dissolved oxygen problem. It is more likely your pleco is simply gulping in air to help with a buoyancy issue.

What Causes Buoyancy Issues In Plecos?

Fish control their buoyancy—i.e. their movement upwards and downwards in the water column—via a special organ called a swim bladder (Wikipedia).

A number of things can cause swim bladder issues in aquarium fish. The most common cause is a dietary issue that has caused constipation. The reason constipation causes a swim bladder issue is because the blockage in the digestive system builds up. In building up, the stubborn poop takes up space in the fish’s abdomen, thereby preventing the swim bladder from inflating and deflating (i.e. stopping the fish from controlling its own buoyancy).

Feeding fresh vegetables like this broccoli can low oxygen through the excess food decaying in the aquarium.

Another common swim bladder issue is caused when females are carrying eggs. The build up of eggs in the female’s body has the same impact on the fish as constipation.

And finally, some strains of fish are predisposed towards swim bladder issues. While this isn’t present in pleco species and domestic strains, it does affect other ornamental fish. Fish bred to have “short bodies” are actually missing a number of vertebrae in their spines, this in turn causes the fish to have a shorter body. Having a shorter body means that the fish’s internal organs have less small in the abdominal cavity. And, you guessed it, this prevents the swim bladder from inflating and deflating naturally. Some examples of this include fancy goldfish and bonsai flowerhorns.

My Plecos Gulp At The Surface During Water Changes – Why?

Plecos will gulp at the surface during water changes for two reasons. One is much more likely than the other, though.

A pleco gulping at the surface during a water change could be to do with temperature change, and thereby lower oxygen content in the water. This is because oxygen levels in water are affected by the temperature of the water.

However, the more likely reason that your pleco—or any fish for that matter—is gulping at the surface during a water change is to do with the chemical reaction associated with dechlorinator. During the chemical reaction, the water condition coopts oxygen for a short time so as to eliminate chlorine and/or chloramine. This is very temporary, though. Shortly after neutralizing chroline/chloramine, the oxygen then becomes available again for your fish to respire.

In order to avoid this, consider mixing dechlorinating your water prior to adding it to the tank and giving it a moment or two for the chemical reaction to complete.

One Last Thing: Beware Of Jumping

Since plecos rush to the surface, gulping for air, there is always a chance they might accidentally jump out of the aquarium. So, keep this in mind and make sure you have a well-fitting lid for your fish tank.

Further Reading