Cory Catfish that keep dying is a problem that many fish keepers have. These very sensitive fish can die because of various reasons, so it’s sometimes hard to get to the bottom of the problem.

From starvation to diseases, we’ll cover everything and more in this full guide.

Signs Your Cory Catfish is Dying

Cory catfish are lively and curious fish by nature. A healthy cory catfish should be scavenging through the tank for food and regularly gasp for air. It should also look healthy and react to changes made in the tank. 

Because of this typical behavior, it’s mostly not that hard to pick up abnormal behaviors. Here are  7 signs of sick or dying cory catfish.

Slow swimming

If your cory catfish is acting in one of the following ways, it might be sick or stressed, possibly causing death if nothing is done:

  •  It barely moves or isn’t scared when touching it (in the water)
  • It lays on its side
  • It lays upside down
  • It floats at the surface
  • It doesn’t move at all 

This abnormal behavior can have various reasons. The most common causes are the water parameters or that it’s too stressed. Scroll down to “Why Do Cory Catfish Die” For More.

Strange swimming patterns

Apart from acting slow or not lively, the opposite of it can also be a sign of a dying cory catfish.

The following swimming patterns are considered abnormal:

  • A Cory Catfish should swim straight and balanced. When it swims sideways or upside down, something is wrong.
  • Sudden impulses of very active swimming, followed by it laying exhausted on the bottom of the tank. 
  •  Swimming at the top of the tank, gasping for air. This is most likely the cause of swim bladder problems or low oxygen levels.

Not eating

When food is added to the tank, cory catfish should become very active and search with their barbels for food. If your cory catfish doesn’t react to any food, somethings wrong. 

Sometimes though, cory catfish can take a while to adapt to your tank. It can take up to a couple of days for them to start eating. 

If your fish are wild-caught, there’s a chance they don’t know that pellets are food. You can try feeding them live foods such as bloodworms to see if they react to that.

Various reasons or diseases can cause Cory catfish not to eat, but if nothing’s done, this will ultimately lead to starvation.

If your cory catfish aren’t eating, I highly recommend reading my full guide on why this is the case:

Read: Why Cory Catfish Don’t Eat >

Gasping at the surface or breathing fast

When you look at the cheeks of cory catfish, it should look like it’s chewing and its gills should always be moving. If the gills move abnormally fast, though, this can be a cause of bad water parameters.

If your fish is gasping at the surface, your water most likely has too little dissolved oxygen in it. This can be caused by rising temperatures or a bacterial bloom. Make sure your filter creates a moving surface, and add an airstone.

Cloudy eyes

A normal healthy Cory Catfish

If you notice your fish having cloudy eyes, you should immediately take action. This is most likely the result of an infection or physical injury. Depending on what causes the cloudy eye, it can go away naturally or your fish might die of it.

Thus treatments for this vary, but I suggest you read this article to get to the bottom of this problem or contact a vet.

Damaged barbels

Healthy cory catfish have long and very sensitive barbels. These barbels are crucial for finding food and eating. Thus, if they can’t use these your catfish might starve. Cory Catfish have 6 barbels.

If you notice your Corydoras having very short or seemingly damaged barbels, this can cause starvation. 

This is most likely the result of sharp gravel. Cory catfish are made to dig through sand to look for food and sharp gravel might cause microscopic wounds causing damaged barbels. Add sand to your tank to prevent this. Sharp gravel in combination with poor water quality causes bacterial infections, which cause barbels to die off.

Another thing you can do is provide foods that don’t fall apart and stay compact. This way cory catfish will have to dig less in the gravel. But even then, adding sand is the safest choice.

Read the full guide on cory catfish barbels.

Unhealthy barbels
Healthy barbels

Damaged fins

Cory catfish having damaged fins isn’t necessarily a sign it’s dying, but it can be.

If the fins have small cuts or pieces out of it, the fish has probably been wounded by a sharp object or other fish. Pay attention to dominant tank mates to prevent this from happening again.

There is however a more serious cause for this too: fin rot. Scroll down to diseases to know more about this deadly disease.

How to know if a Cory Catfish is dead

Before flushing your cory catfish through the toilet, you should obviously make sure it isn’t alive anymore. 

The definitive way to check if your cory catfish is still alive is by looking at its gill movement. If your cory catfish doesn’t breathe (which result in its gills moving), it’s death.

If it does move its gills, there are two options:

  • Trying to cure the disease or trying to save it.
  • Euthanizing it. Sometimes, the fish is damaged too hard to revive. Euthanizing is the most humane option. Don’t freeze it alive or flush it down the toilet, but add it to a container of water with clove oil. this is the most humane way for fish to die.

Why do Cory Catfish Die?

There are often multiple things that can cause the same symptoms. So after examining the behavior of your cory catfish, you should act quickly and find the reason for it.


These C. oiapoquensis are too skinny. As you can see, they don't have a teardrop shape.

Because cory catfish are often sold as the ideal cleaner fish or algae eaters, there’s a popular misconception that they don’t need any extra food. And let us be clear: cory catfish do neither of both.

Cory catfish should always be fed specialized sinking foods, and enough of it so tank mates don’t outcompete them.

Another reason for starvation may be that the catfish’s barbels are damaged. These are vitally important for them to look for food.

Corydoras often face a slow death because of starvation, without any visible symptoms. this makes many people think their catfish died a ‘sudden’ death.

In reality, you can easily know whether your catfish is underfed or not:

  • When looking from above, cory catfish should be round (teardrop shape), and look full. Males are slimmer than females, though.
  • If you feed your fish, but it won’t take any food, this ultimately causes starvation. Try adding live foods, or observe for any other odd behavior.


The Full Guide To Cory Catfish: Tips & Tricks

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Water parameters

Believe it or not, cory catfish are actually very sensitive fish. Both to fluctuations in these parameters or not optimal conditions.

First off, it’s vital to buy a special water testing kit. 

These come in a couple forms: digital, strips and drop tests. I recommend the strips as these are the cheapest and easiest to use. Check test kit out ->


NitrIte (NO2) is extremely toxic for all aquarium fish. This ion is transferred into nitrAte, which can be absorbed by plants. 

If there aren’t enough bacteria to convert this nitrite into nitrate, a so-called nitrite peak occurs, which is deadly for fish.

Nitrite peaks occur after two to three weeks of your tank cycling. This is the “New tank syndrome”.

You can recognize nitrite poisoning by the following symptoms:

  • Your fish is gasping for air (although this can be caused by other things, too).
  • Fish trying to jump out of the tank.
  • Color loss
  • Pinched fins

If you think you are dealing with a nitrite peak, immediately perform a >50% water change and a test. Nitrites should always be 0. Higher values may be deadly.

Image source: Aquascaping Lab


Nitrates aren’t as deadly as nitrites, but should always be below 40 ppm, and preferably below 30 ppm. Any higher values can cause nitrate poisoning.


Normal ammonia values are 11 to 32 µmol/L. Anything above that might cause organ dysfunction, problems with breathing, and eventually death. 

An ammonia peak is caused by too many organic materials breaking down, without enough filtration or bacteria to deal with it. If you notice high ammonia values, an immediate water change should be done.


In the wild, cory catfish live in streams where the pH is anything between 3 and 7. Most bred cory catfish prefer different parameters, because they have gotten used to regular tap water. 

They do fine in tap water at pH levels from 6 to 7,5. You should start to worry when your pH is above 8 or below 4, which is uncommon but it can happen.

It’s recommended to add RO water in this case. This has pH 7, and (temporarily) adding it gives you time to get the cause of this.

Water temperatures

The ideal temperature range for cory catfish is between 74°F and 80°F. They don’t do well at room temperature so you will need a heater. Some species like C. sterbai can be at higher temperatures of max. 86°F.

If your water temperature is too warm or too cold, this will result in stress for the fish and changes in behavior. Over the long-term, this can cause diseases or death.

Diseases / parasites

This is by far the most likely reason for your cory catfish to die. Diseases come in many forms and there are a lot of parasites known in the aquarium hobby.

To examine what your fish are suffering from, read the diseases part in this blog post. 


Cory catfish are lively and fun fish, but only when their tank is suited to their needs. In many cases, cory catfish suffer from severe stress causing death.

This stress can be caused by many things but it’s most likely one of the following:

  • Not being kept in groups

Cory catfish are group animals, and they should always be kept in a group of at least 6 individuals of the same species. this has a direct link with their tank size because you need at least a 20-gallon tank to house such a group.

When you keep less than 6 fish together, the cory catfish will not feel safe, which causes unnatural behavior and stress.

Read how many cory catfish should be kept together for more.

  • Wrong tank mates

Even though cory catfish are very peaceful fish that can live with most other fish, it can still be that they are being harmed by their tank mates. Some fish can outcompete cory catfish for food, or even attack the fish. 

This will mostly be the result of the two following points, otherwise, you have to separate your fish asap.

  • Tank size

The minimum tank size for cory catfish is 20 gallons. Some smaller species can be kept in 10-gallon tanks, but common types like albino cory catfish need 20 gallons to be housed in a group of 6.

  • Not enough/bad natural cover

It’s a common occurrence to see cory catfish being kept in barely decorated tanks, without any live plants or natural structures. This however creates stress and might result in very shy behavior. It might seem contra-productive, but adding hiding places makes the fish less shy and more comfortable.

In contrast to fake plants, add live plants. And in contrast to the fancy sponge bob house, you bought in the pet store, add a piece of driftwood or a stone. 

Lastly, pay attention to the kind of gravel you are using. The best choice is a dark-colored substrate or sand. Bright colored gravel kinds like in the picture below reflect too much light color and stress these fish.

Blue gravel stresses these fish and is not a good choice.


It’s not uncommon for cory catfish to go in a “shock” mode. This is most likely because of one of the following two reasons:

  • Low amount of other fish

In the pet store, fish are often crowded in an overstocked tank. Cory catfish will see a lot of movement. When they get added to your tank without any tankmates, they might get shocked or severely stressed. Adding other active tank mates will help this and reduce the stress.

  • Water parameters

Before adding your fish to your own tank, it’s important to climate them first. If you want to be sure, ask the pet store what the water conditions are like, a good store will know this.

Depending on how big the difference is between you and where the fish comes from, the amount of acclimatization varies.

I recommend setting up a separate tub and putting the cory catfish in this. Then add an air tube with a knot in it, so the water from your tank gradually drips in. 


Overstocking is a severe problem when keeping catfish. Mainly because these fish need to be kept in groups and people try to fit the fish in tanks that are too small.

Cory catfish can’t be kept in a 5-gallon tank with 3 guppies and a pleco. Yep, that’s only one piece I read online. As stated multiple times in this blog post, many species need 20 gallons to be healthy and happy.

And even then, you should always do your research and make sure you aren’t overstocking your tank. Overstocking your tank will result in a food competition, high waste levels, and conflicts between fish – a no-go!

Read our article on how many cory catfish to know how many cory catfish can be kept in your tank.

How To Prevent Cory Catfish From Dying

Cycle Your Tank

Cycling a tank is crucial for its success and keeping fish successfully in it. Without cycling, there isn’t a biological balance in the tank, and there are no beneficial bacteria.

These bacteria are crucial for the nitrogen cycle, which transforms fish waste into NO2 into NO3, which can be absorbed by plants. 

It’s also important to let your tank cycle for at least three weeks, because of the new tank syndrome. This causes a nitrite peak, deadly for fish.

After this period, the water parameters should be stable and there will be a biological balance in your tank.

Quarantine fish

When getting new fish, quarantining them is a crucial step to make sure no diseases are brought into your tank.

Especially if your pet store doesn’t quarantine fish themselves, quarantining fish is recommended. 

Use sand

As we discussed before in this article, sand is the best substrate for cory catfish.

Why? Cory catfish are bottom dwellers, that dig through the substrate looking for food. If you use sharp gravel, their barbels might be damaged (which is a sign your cory catfish is dying). 

Even though cory from Aquarium Co-Op is said to have seen cory catfish in the wild living in sharp gravel, it’s still the safest choice to put fine sand in your tank.

If you really don’t like sand, you can use rounded gravel, too. Cory catfish will not dig as much in this, but it will not harm their barbels.

Feed A Varied Diet

One of the things I see a lot of people do wrong is feeding their cory catfish a bad diet, or sometimes providing no additional food at all.

Because cory catfish are not competitive feeders, other fish might outcompete them. To prevent this from happening, buy pellets that instantly sink to the bottom.

Another big misconception is that cory catfish eat algae. Although they’re not picky eaters, cory catfish are primarily carnivorous, so they should be fed with various meaty foods for them to get enough nutrition. I highly recommend reading my full guide on the ideal cory catfish guide. Read the article.

Examples of good foods are shrimp pellets, Hikari Vibra Bites, various live foods, Hikari Sinking Wafers, and Repashy. Algae wafers make less ideal food, due to the low protein count.

Test Your Water

The key to a healthy ecosystem for cory catfish is regularly testing your water. Even if nothing seems to be wrong, it’s always useful to check on possible problems.

And when there is seemingly something wrong in your tank, always test as fast as possible so you can track down the source of the problem.

I recommend buying a test kit so you can easily and quickly check on various parameters such as pH, nitrites, nitrates, and ammonia. 

Perform regular water changes

In optimal condition, you should weekly change the water of your tank. Your filter can’t take on all waste, so changing water on a regular basis provides your fish with new clean water.

If you don’t change your water, ammonia and nitrates will start stacking up. In high concentrations, your fish can die because of these.

Always make sure to add a water conditioner to tap water first, to neutralize any possibly harmful chemicals. 

Buy healthy fish

It might seem obvious, but it’s really not. 

If you are planning to buy cory catfish for your aquarium, you should always pay attention to the health of the fish you are buying.

Even if you just set up the perfect tank for cory catfish, this will not matter if you buy sick fish in the first place. Unfortunately, it’s common for big stores like Petco or Petsmart to sell weak stock, so I recommend going to a local fish shop or breeder to get the highest quality.

Here are a few tips to buy healthy fish:

  • Fish should have a bright color pattern, with full scaling and healthy fins
  • Stay away from tanks with dead fish in the tank.
  • Look around at the tanks in the store. Are they clean, are there any sick fish in the store?

The product which has helped me the most in my fish keeping journey are Indian almond leaves

I use them in all kinds of circumstances, but the main benefit they offer is that they add tannins to the water, which then again help prevent infections and diseases.

Apart from this, the tannins improve the water quality and attract a lot of microorganisms, helping the overall ecosystem.

Check out my preferred leaves on Amazon.