Why Cory Catfish Keeps Swimming to Surface?

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As bottom dwellers, Corydoras aren’t known for their surface swimming. These fish will stick to the substrate as that’s their primary feeding ground and safe space at the same time.

You will rarely see your catfish venturing beyond the tank’s mid-section, but this may not always be the case.

In some cases, Corydoras will swim to the water’s surface quite frequently, which is atypical but not necessarily worrying.

Let’s see what drives that behavior and whether you should be worried.

Reasons Corys are Swimming to the Surface

Believe it or not, even bottom dwellers sometimes go to the water’s surface. This behavior is more prevalent among catfish species like Corydoras, but it’s not always innocuous.

So, let’s look at some of the reasons why your cory catfish may reach the water surface more often.

Buoyancy Regulation

This is a normal behavior that links to the corydoras’ physiological makeup. Corydoras are known as intestinal breathers, which, just like labyrinth breathers, require atmospheric air from time to time.

The process is just different, as Corydoras don’t have a labyrinth organ like bettas. Instead, they use their intestine’s capillaries-filled wall to assimilate oxygen and transport it directly into the bloodstream.

The influx of extra oxygen allows Corydoras to manage their buoyancy properly, so they can navigate their environment more effectively.

This adaptation forces corys to regularly go to the water surface to refill their oxygen reserves.

Low Oxygen Levels

You may have heard that Corydoras are very resilient and can adapt to poor water conditions, which is true. This doesn’t mean that they are impervious to any water parameters, however foul.

We’ve already discussed the Corydoras’ amazing breathing abilities, which allow them to breathe atmospheric air whenever the oxygen levels in the water drop.

If you notice your corydoras swimming to the water’s surface to breathe too often, consider the amount of dissolved oxygen in the water.

Verify the oxygen levels and have some solutions ready to implement, such as:

  • Adding more live plants for a natural influx of fresh oxygen during the day
  • Perform an immediate water change to refresh the environment and boost oxygen levels
  • Adopt a weekly water change routine to keep oxygen levels constant
  • Use air stones if the habitat is currently suffocated due to a lack of oxygen
  • Monitor the ecosystem closely to prevent drops in dissolved oxygen over time

Ammonia Problem

This is a clear matter of life and death, given that ammonia is essentially toxic to fish. Ammonia is naturally-occurring in all aquatic ecosystems, but it’s more prevalent in catfish tanks.

This may sound paradoxical, given that catfish contribute to a healthier and cleaner environment, but it will make sense in a second.

You see, it all relates to the type of substrate you’re using, i.e., sand. Sand is necessary for Corydoras, given that these are sand-sifting fish that constantly look for food on and in the substrate.

The problem is that sand requires constant maintenance to prevent the formation of anaerobic pockets.

These are the result of the sand’s compaction rate, given that sand has small and fine particles that allow for little-to-no water circulation between them.

Anaerobic pockets form underneath the sand due to bacteria consuming decomposing matter and producing ammonia and other poisonous gases.

These pockets are sometimes visible through the tank wall, but often times they’re not.

Anaerobic pockets accumulate ammonia which the catfish will inevitably release during its usual substrate incursions. The result is a sudden ammonia bath that could send your catfish into ammonia shock.

If that doesn’t happen, the ammonia will be released into the water column, forcing the fish to flee the area.

The fish swimming to the water’s surface to breathe is the first sign that something’s not right. This is due to the excess ammonia causing suffocation.

Soon, other signs will follow, such as discoloration, lack of appetite, red skin patches, red or bloody gills, erratic swimming patterns, etc.

To prevent the problem, consider stirring the substrate gently from time to time to prevent the formation of ammonia pockets.

A good chemical filtration system is also necessary to cleanse the tank of any harmful chemicals that may seep into the water column.

Disease or Parasites

Catfish can struggle with parasites and various diseases when kept in subpar water conditions. This is generally the result of stress, as stress is known to affect the fish’s immune system.

A sick catfish will display an array of symptoms, depending on the nature of the disease.

These include rubbing against rocks (more prevalent in the case of skin parasites), lack of appetite, hiding behavior, swimming to the surface (in case of infected gills causing respiratory problems), etc.

The nature of the treatment depends on the disease’s profile and severity. You might need to quarantine your catfish if it shows signs of parasitic, bacterial, or fungal infections.

These can spread to other tank occupants fast.

Ich is especially concerning in this sense, given that the parasite undergoes several growth cycles.

If your catfish is infected with Ich, you might need to disinfect the entire tank and quarantine all fish for treatment.


This is the final and most important entry on today’s list.

Corydoras can experience stress for a variety of reasons, such as:

  • Sickness or parasites
  • Feeling lonely
  • New Tank Syndrome
  • Improper dieting
  • Aggressive mates
  • Improper tank layout, etc.

The sooner you address your catfish’s stress, the faster the fish will recover.

To do that, consider the following options:

  • Personalize the catfish’s habitat – Corydoras are timid and peaceful animals that like to stick to the shadows. They rely on their habitat to hide when attacked or bothered by other life forms that share the same living space. Add live plants, caves, rocks, and any other decorative elements that corys can use for cover.
  • Choose their tankmates carefully – You want to stay away from aggressive or overly energetic fish species that will bother your Corydoras often. You also want to avoid large fish species that could eat your catfish and fast eaters that will create an overly competitive environment. Corydoras rely on food leftovers from other fish to satisfy their scavenging itch. Competitive eaters will even consume Corydoras’ food before reaching the substrate, so that’s another problem you should consider avoiding.
  • Keep corys in groups – Corydoras can survive on their own in the tank, but they require the presence of other corys to feel happy and calm. These are social animals that enjoy interacting with members of their own species. Just make sure there’s enough room to accommodate all catfish, along with the necessary decorations and tank equipment. Overcrowding can stress your catfish, and we’ve already discussed the dangers associated with this issue.
  • Preserve water quality – While corys are adaptable and resilient, they don’t fare that well in subpar water conditions. Change their water at least once every 2 weeks and clean the substrate regularly. The goal is to preserve the system’s stability to prevent ammonia buildup. Proper water oxygenation is also necessary for a fresh and healthy aquatic setup.
  • Adequate diet – Corydoras can become stressed when starved or when experiencing nutritional deficiencies due to poor diets. These fish are omnivorous, so they require a balanced and varied diet to remain healthy and in good spirits. Don’t rely on them getting their nutrients from their scavenging incursions. Even tank cleaners like catfish require extra food to fulfill their nutritional needs.


While catfish will swim to the water’s surface to meet their physiological needs, they shouldn’t do it too often.

Maybe several times per day should be enough. If your Corydoras engage in that behavior more often than normal, consider some of the explanations and fixes I’ve offered today.

Test things out and post your results so that others can learn from your experience.

By the way, cover your tank with an aerated lid if your Corydoras keep going to the surface.

They can jump out if water conditions are inadequate or the fish is simply stressed enough.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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