Cory Catfish Died Suddenly? Here’s Why It May Have Happened

Last Updated on March 22, 2022 by cmoarz

Nothing sucks more than waking up one morning only to discover your Cory Catfish has died. But often enough there are no apparent reasons why this may have happened. So why did your cory catfish die suddenly?

If it makes you feel any better, Cories dying suddenly is not uncommon. Most of these reported deaths affect new cories that have just been purchased, rather than older cories.

This happens for a variety of reasons which we will get into below, But it’s definitely not uncommon.

Some of the main causes for a single cory death

The main and most reported sudden cory deaths are presented in newly purchased corydoras. It is not uncommon for fish stores to stock their tanks with fish that were captured in the wild, or raised in poor conditions.

They often carry many genetic disorders, internal parasites, infections, and diseases that make their already fragile health even more perilous.

Add to that the less than stellar care these corydoras may have received from shipping, stocking, and general care of the fish provider themselves, it would seem like they have the deck stacked against them.

It’s not uncommon for a store to buy their fish from a wholesaler, who got them from another store, who got them from another store, and so on. So by the time the fish reaches your local pet shop, it has been through quite a bit of stress which can take its toll.

Then you factor in the often poor water quality of a pet store’s tanks, as well as the stress of being transported and handled by several people, it’s no wonder that many of these fish don’t make it.

Corydoras are already very fragile when first brought into a home aquarium. When all that additional stress and health issues are stacked, including the possibility of a sick, wounded, or stressed corydoras poisoning itself, these store-bought cories will often perish.

Usually within 1-2 weeks after purchase.

The main causes of corydoras death in an established home aquarium are much less dramatic and include the following:

  • Old age
  • Internal parasites
  • External Parasites (Ex: ich)
  • Lack of environmental enrichment
  • Poor water quality (usually affects all corydoras in a tank, but unhealthy ones may get hit faster)
  • Physical injuries, including being stuck under a decoration or being sucked into the filter intake, and burns from being stuck behind heaters
  • Diseases, such as columnaris, kidney disease, and swim bladder disease
  • Self-harm accidents (Ex: Smacking into the side of the glass tank or jumping into the aquarium cover)
  • Lack of food

This is often seen in tanks with large predatory fish that monopolize all the food, leaving the corydoras with nothing to eat.

There is no shortage of ways these fish can die, but the most common are mistreatment and bad quality of care from pet shops and supply chain providers.

Main causes for a group of cories dying all at once

When you see multiple cories die suddenly at once time, it can still be caused by pet store mismanagement if they are new, However, if they are seasoned tank fish, a larger problem could be at play.

The first thing you should always do in these situations is to check your water parameters and temperature.

They should match whatever parameters your specific species of corydoras requires.

Bad water and too high or low of a temperature are major stressors on these fish and can lead to a mass death scenario.

If your water quality is fine, the next thing you should look at is what else changed in the tank around the time of their death.

Did you add any new fish? Change the decor? Have a power outage?

All of these things can affect your tank and in effect your fish.

If you’ve medicated recently then is it possible you’ve overdosed on your fish? Or perhaps they aren’t compatible with the medication you used and are sensitive to it.

All of these things can play a role in the sudden death of your fish, especially with multiple casualties.

It’s important to always rule out the most common causes before moving on to more serious possibilities.

If you’re still at a loss, consider taking a water sample to your local fish store or contacting a professional for help.

If there are any remaining fish in the tank, consider moving them to a new quarantine tank and getting them out of the environment that had the mass death occur.

Corydoras are very sensitive to changes in their environment and even a small change can be stressful for them and not other fish.

When cories die, it’s important to try and figure out why so you can take the necessary steps to prevent it from happening again in the future.

While there are many potential causes of death, the most common by far is poor water quality and mistreatment from pet shops.

Be sure to keep an eye on your water parameters and tank conditions, and if you see any changes, take corrective action right away.

This will help ensure the long-term health of your corydoras and all the other fish in your tank.

If you find you’ve lost multiple fish from the same pet shop, consider buying from another source in the future.

It’s always better to err on the side of caution when it comes to your fish, and if something doesn’t seem right, it probably isn’t.


Owner of and also owner of actual Aquarium Gravel believe it or not! ;). Setting up beautiful aquarium sceneries and habitats since I was very young. Enjoy!