How Many Cory Catfish in a 40 Gallon Tank (160 Liters) Should You Have? - "Corydoras aeneus" by WIKIFAN-UL (selbst fotografiert) is licensed under CC BY-SA 3.0.
How Many Cory Catfish in a 40 Gallon Tank (160 Liters) Should You Have? - "Corydoras aeneus" by WIKIFAN-UL (selbst fotografiert) is licensed under CC BY-SA 3.0.


When it comes to setting up an aquarium, one of the most delightful choices you can make is to include cory catfish, those peaceful and industrious little cleaners of the aquatic world. Their social nature and fascinating behaviors make them a favorite among aquarists. However, a common question arises: “How many cory catfish in a 40 gallon tank should I have?” This question is not just about numbers; it’s about creating a harmonious environment that caters to the needs of these charming creatures while considering the dynamics of a community tank.

About Cory Catfish

Cory catfish, or corydoras, are those charming little bottom-dwellers you might have seen darting around in freshwater aquariums. With their armored bodies, these peaceful fish carry a certain knightly elegance. They come in various colors and patterns, but most have a sleek, shimmering appearance that can range from silver and gold to green, bronze, and even multicolored.

What truly sets cory catfish apart, though, is their adorable behavior. They’re incredibly social and thrive in groups, often seen scuttling along the bottom of the tank in a cute, bustling convoy. Their barbels, or whiskers, help them sift through the substrate to find food, giving them the appearance of little vacuum cleaners tidying up the aquarium floor.

Cory catfish are also known for their quirky “cory dance.” It’s a sudden, spirited dash to the water’s surface to gulp air before quickly returning to the bottom. This behavior is normal for them, thanks to a neat evolutionary trick that allows them to breathe atmospheric air when needed.

In essence, these fish are the peaceful, hardworking janitors of the freshwater community tank, adding a dash of charm and industriousness to their aquatic world. They’re not just about cleaning up; their friendly nature and social antics make them a delight to watch and a favorite among fish enthusiasts.

Should You Keep Them in Groups?

Keeping cory catfish in groups taps into their natural behaviors and needs in several compelling ways. In the wild, these delightful bottom dwellers are found in schools, navigating together through the waters of South America’s rivers, streams, and flooded forests. This schooling instinct is deeply ingrained in their behavior, influencing not only their sense of security but also their overall well-being in an aquarium setting.

So, why keep them in groups? Here’s a deeper dive:

  • Social Interaction: Cory catfish are incredibly social creatures. In a group, they communicate and interact with one another in ways that are vital for their social health. This interaction includes everything from foraging together to playfully chasing each other around the tank. It’s a part of their natural behavior that solitary living simply cannot replicate.
  • Stress Reduction: Like many schooling fish, cory catfish feel safer and more secure when they are part of a group. This safety in numbers helps reduce stress, a critical factor in maintaining their health. Stressed fish are more prone to diseases and often have a shorter lifespan. By keeping them in groups, you mimic their natural environment, providing them with the comfort and security they need to thrive.
  • Enhanced Activity: Cory catfish are more active and exhibit more natural behaviors when they’re in a group. This increased activity is not only healthier for the fish, but it also makes for a more entertaining and engaging aquarium for observers. You’ll see them exploring all corners of the tank, engaging in playful behavior, and even synchronized swimming, which is both fascinating and delightful to watch.
  • Breeding Behavior: For those interested in the breeding aspect, cory catfish are more likely to breed in an environment that closely mimics their natural habitat. A group setting can encourage spawning behavior, offering enthusiasts a chance to observe and perhaps even assist in the breeding process of these charming creatures.
  • Collective Foraging: In a group, cory catfish can more effectively forage for food. Their natural behavior of sifting through the substrate is better facilitated in numbers, ensuring they all get a chance to find food. This group foraging behavior also helps in keeping the tank cleaner, as they’re more efficient in scavenging leftover food and detritus from the bottom.

In essence, keeping cory catfish in groups not only fulfills their natural need for companionship but also significantly enhances their quality of life. It transforms the aquarium from a mere holding space into a vibrant ecosystem where these fascinating creatures can exhibit their full range of behaviors, contributing to a healthier, happier life for them and a more delightful viewing experience for you.

How Many Cory Catfish in a 40 Gallon Tank (160 Liters) Should You Have? - "Corydoras aeneus" by WIKIFAN-UL (selbst fotografiert) is licensed under CC BY-SA 3.0.
How Many Cory Catfish in a 40 Gallon Tank (160 Liters) Should You Have? – “Corydoras aeneus” by WIKIFAN-UL (selbst fotografiert) is licensed under CC BY-SA 3.0.

How Many Cory Catfish in a 40 Gallon Tank (160 liters)?

So, how many cory catfish in a 40 gallon tank (160 liters) should you keep? In a 40-gallon aquarium (160 liters), you’ve got a decent amount of space to create a comfortable and engaging environment for cory catfish, along with a selection of other tank mates. The key to stocking an aquarium is to ensure that it’s not overcrowded, providing enough room for all inhabitants to swim freely and have their own space, which is crucial for their health and stress levels.

For cory catfish specifically, since they should be kept in groups of at least 5 or 6 to ensure their social and behavioral needs are met, a 40-gallon tank (160 liters) can comfortably accommodate a group of about 6 to 8 cory catfish. This number can vary slightly depending on the species of cory catfish you choose, as some species are smaller and others can be a bit larger. Smaller species like Pygmy Corydoras (Corydoras pygmaeus) could allow for a larger group, while larger species like the Bronze Corydoras (Corydoras aeneus) might mean sticking closer to the minimum group size recommended.

When considering other tank mates, it’s important to choose species that are compatible with cory catfish, meaning they are also peaceful and thrive in similar water conditions. Good companions could include small to medium-sized tetras, rasboras, and danios, which tend to occupy the middle to upper parts of the tank, leaving the bottom for the corys. It’s also beneficial to include some surface-dwelling species and perhaps a few peaceful bottom-dwellers or mid-level swimmers to create a balanced community.

The exact number of additional tank mates will depend on their size and requirements. It should be adjusted based on the specific needs of the fish, including their adult size, behavior, and the tank’s filtration capacity. Remember, it’s not just about the physical space but also about the biological load on the tank’s ecosystem.

To avoid overstocking, start with the cory group and then gradually add other species, monitoring water quality and fish behavior closely with each new addition. Ensure your filtration system is adequate for the bioload, and keep up with regular maintenance, including water changes and substrate cleaning, to keep the environment healthy for all inhabitants.

A 40-gallon tank (160 liters) offers a great opportunity to create a diverse and lively community aquarium. With thoughtful selection and careful planning, you can ensure a harmonious home for your cory catfish and their tank mates, providing you with a beautiful and engaging aquatic display.


Determining how many cory catfish in a 40 gallon tank (160 liters) to keep, is essential for creating a balanced and thriving aquarium. A group of 6 to 8 cory catfish can comfortably live in such a space, offering them the social interaction they need without overcrowding the tank. This, combined with a careful selection of compatible tank mates, ensures a vibrant community where all inhabitants can flourish. Remember, a well-planned aquarium goes beyond aesthetics, contributing to the health and well-being of its aquatic residents. By adhering to these guidelines, you’ll create not just an aquarium, but a thriving ecosystem that brings joy and tranquility to any space.