Why is My Cory Catfish Not Eating?

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Corydoras are peaceful, calm, and shy fish that can thrive on pretty much any food. They rank as omnivorous bottom dwellers but generally occupy the tank’s lower and mid areas.

It’s normal for the fish to exhibit slight changes in appetite depending on the food it’s getting and the quantity.

But what happens if your fish refuses food altogether? This isn’t normal behavior, so let’s deconstruct it to find out what’s happening.

7 Reasons Cory Catfish is Not Eating

Corydoras are among the more sensitive fish species. They can sometimes experience health problems and behavioral issues for a variety of reasons.

These reasons can also cause them to refuse food and showcase lethargy and signs of stress.

Today, we’ll look into 7 of the most compelling reasons that could alter the fish’s behavior and overall wellbeing:

1. Poor Water Conditions

Corydoras are adaptable fish, generally speaking, but they require stable and optimal water conditions to thrive.

Degrading water parameters will affect the fish’s behavior and health over time.

To prevent or fix the problem, you should always:

  • Have a filter installed – The filtration system eliminates floating particles like food residues, fish waste, and decaying organic matter, keeping the water cleaner and fresher. It will also boost oxygenation and provide the Corydoras with subtle water movement to support their breathing.
  • A good maintenance routine – Corydoras aren’t particularly messy fish but require regular maintenance and tank cleaning. You should vacuum the substrate occasionally, remove dead plant matter, and clean any excessive algae deposits that could muddy the water.
  • Prevent overfeeding – Overfeeding is the most common cause of water quality degradation. Corydoras usually feed on food leftovers from other fish, but not even they can eat everything. Only feed your fish sufficient food for them to consume in 1-3 minutes, depending on the species. If you only have Corydoras in your tank, pay attention to how much they’re eating on average and stick to that to minimize the amount of food residues.

2. Cory is Acclimating

This is a natural phenomenon and generally not a reason for concern. However, it can become one. Corydoras, and all fish in general, require time to acclimate to their new environment.

During this time, they may exhibit signs of stress and lack of appetite, which is normal under these circumstances.

The problem is that some Corydoras can even die due to the acclimating stress. The fish has been on the road for a while, and then it’s forced to adapt to a completely new environment.

This can quickly overwhelm the catfish, so you need to approach the situation more carefully.

You should acclimate your Corydoras gradually to allow the fish the time it needs to accommodate to its new setup. The acclimation process is easy, but it can take some time.

In this sense, you need to:

  • Place the fish bag into the tank water for 20-30 minutes – This is to allow for proper temperature transfer between the bag and the tank water.
  • Add tank water into the fish bag – You perform a small cut in the bag’s upper area above the tank’s water surface. You then add small amounts of tank water through the opening every 4-5 minutes. If the bag fills up, empty some of it out (not in the tank) and restart the process.

The acclimation process should be complete after those 30 minutes have passed, at which point your catfish will be ready for release.

3. Bullied by Tankmates

Corydoras are peaceful animals that prefer to avoid stressful or combative situations. You should always pair them with equally peaceful tankmates to prevent bullying or territorial-based attacks.

Aggressive and territorial tankmates can attack or bully your Corydoras, which can cause significant stress.

Corydoras are known as armored catfish thanks to their armored plates covering their body. So, it’s unlikely that other fish can hurt them physically. But they can stress them out, and fish stress is a notorious killer.

If you notice signs of bullying or straight-up violence between your catfish and other tank residents:

  • Change up the environment – Add more live plants, more rocks, more decorations, and more anything-that-can-serve-as-hiding-spot. Your Corydoras will use their environment to hide and break line of sight with their aggressors.
  • Tweak water quality and diet – Maybe the fish are angry due to improper tank conditions or insufficient or poor food. Look into those issues and see if the situation improves.
  • Eliminate the aggressor(s) – If nothing else works, it’s always better to eliminate the aggressor from the environment and bring in more peaceful residents.

You can easily avoid this issue by only housing Corydoras with peaceful and calm fish species.

4. Disease or Parasite

Corydoras aren’t particularly sensitive to any specific conditions. But they can struggle with typical freshwater conditions like Ich or fungal infections.

These result from poor water conditions, improper food, and constant stress, weakening the fish’s immune system.

There are 2 core notions to consider when it comes to dealing with sick Corydoras

  • Early treatment – The idea here is to identify the early signs of infection, quarantine the sick fish, and ensure proper treatment to cut the disease short. Don’t skip the quarantine part, no matter how mild the infection seems. If it’s contagious, other fish will get it, creating more problems than you’d like to handle.
  • Prevention – This is a straightforward concept, as it refers to providing your catfish with optimal and stable water conditions. Keep water parameters in the optimal range, clean the tank regularly, prevent overfeeding, and don’t overcrowd your fish.

Most importantly, always observe and learn your fish’s behaviors so that you can identify early signs of disease.

In advanced phases, most fish infections and conditions are fatal, and early detection is key to a swift recovery.

5. Overcrowded Tank

Corydoras grow between 1 and 4 inches and like to live in schools. It’s not absolutely necessary to keep them in groups, but these are social fish that live longer, healthier, and happier in a community. So, I guess, it is necessary to keep them in groups.

The standard recommendation in terms of tank size is 20 gallons for a group of 4-5 Corydoras, but this depends on the fish’s size.

I would recommend 30 gallons, especially if your catfish are closer to 4 inches in size. Stick to this golden rule, and don’t overcrowd your fish.

All fish have minimal swimming space requirements to remain healthy, comfortable, and stress-free in their habitat.

Overcrowding is a slow killer, causing stress, excess fish waste, territorial fights, food-related violence, bullying and fin nipping, etc.

If your fish require more space, remove some of them from the environment or upgrade your tank.

6. Loneliness

We’ve discussed this precise point previously. Corydoras are social animals that enjoy living in schools. Many aquarists form 1-catfish nano tanks due to not wanting to invest in a larger aquarium which is too bad.

Solo catfish are known to live shorter and more unhappy lives than those living in groups.

You should always have at least 5-6 Corydoras in your tank. This allows the fish to interact with each other, causing them to appear more energetic throughout the day.

If you are creating a catfish group, consider the following:

  • The need for sufficient space – We’ve already discussed this aspect. Corydoras aren’t particularly territorial, but they do value their personal space, among other things. I would recommend at least 25-30 gallons for a group of 5-6 Corydoras.
  • Sufficient food – These bottom dwellers will share the same feeding space. You should expect some catfish to eat more than others based on their size, temperamental differences, and hierarchical dominance. Provide your Corydoras with more food and ensure none are starving.
  • Watch out for the males – As peaceful as Corydoras are in general, the situation can change when there’s an outpour of testosterone in the tank. I wouldn’t recommend keeping more than 1 catfish male per tank unless you have a lot of space and plenty of aquatic decorations around. Generally speaking, you should go for 1 male and 4-5 females for a stable and calm group.

If you want to create a sustainable community tank, mixing your Corydoras with other fish species, make sure you choose compatible tankmates similar in size, behavior, and aquatic preferences.

7. Expired or Bad Food

Corydoras aren’t overly pretentious about their food. As omnivorous scavengers, these fish will eat anything, although they do prefer more animal protein than veggies.

They also accept pellets, tablets, and wafers, which can create some unexpected problems along the way.

Many aquarists are used to storing their fish food for a lot of time, often in improper conditions. It’s not uncommon for the food to go bad or expire along the way.

You may not notice any change in the food’s appearance or smell, but your fish will sense the difference.

If the catfish simply refuses its food, verify it to make sure it’s still eatable.


Corydoras are adaptable animals, but even they have their weaknesses to work on. If your catfish displays a lack of appetite, use this article as a reference point.

It provides you with the necessary know-how to identify and manage any problem that your catfish might face.

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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