Quick Answer
Keeping just 2 cory catfish can work but is generally not recommended. Cory catfish are schooling fish that do best in groups of 6 or more. A minimum of 6 cory catfish allows them to properly school, reduces stress, and promotes natural behaviors. While 2 corys may get along fine, they will likely be less active and spend more time hiding. Providing at least 6 corys of the same species allows a proper school to form.
Do Cory Catfish Need to Be in Schools?
Yes, cory catfish are shoaling fish that should be kept in schools of 6 or more. Cory catfish naturally live together in large groups in the wild for protection and companionship. Keeping them in proper schools in captivity allows them to exhibit their natural schooling behaviors. Schools help reduce stress, promote activity, and create a sense of security. Just 2 corys together cannot properly school or shoal.
Reasons to Keep 6+ Cory Catfish
Here are some of the key reasons why 6 or more cory catfish are recommended for a group:
Natural Behavior
Cory catfish naturally live in large schools in the wild. Providing a school of 6+ catfish allows them to exhibit their natural schooling and shoaling behaviors. This includes synchronized swimming, schooling for security, and social interaction. Just 2 corys cannot properly school together.
Reduce Stress
Cory catfish kept on their own or in small groups are more likely to feel stressed and insecure. A proper sized school helps minimize stress by providing safety in numbers and social companionship. Lone corys often hide more.
Increased Activity
Cory catfish kept in schools are more likely to be active and swim around the tank confidently. Groups of 6+ corys will interact, explore together, and utilize the whole aquarium. Just 2 corys may spend more time being inactive or hiding.
Health Benefits
The benefits of schooling for security and companionship promotes the health and wellbeing of cory catfish. Appropriate schools lead to less stress which results in a healthier immune system and longer lifespan. Solo corys tend to be more stressed.
Disadvantages of Just 2 Cory Catfish
While 2 cory catfish may get along, keeping just a pair together has some disadvantages including:
Lack Proper School
Two corys together cannot truly school or shoal together. This inhibits their natural behaviors. They will likely fail to exhibit synchronized swimming or schooling behaviors. A minimum of 6 catfish is needed to form a proper school.
More Hiding
Since a pair of corys may feel insecure, they tend to spend more time hiding than a larger group would. Often a solitary cory or a pair will stay hidden the majority of the time.
Less Interaction
With just 2 corys, there is less fish-to-fish interaction. Cories interact socially in larger groups. A pair is unable to stimulate natural interaction between individuals that comes with a larger school.
Reduced Activity Levels
Since they feel less secure, a pair of corys often shows reduced activity levels compared to a proper group. They are less likely to swim openly around the tank and utilize all areas.
Increased Aggression
Sometimes aggression can occur between just 2 corys as they compete for resources and hierarchy. Forming a larger group helps disperse aggression.
Signs Your Cory Catfish are Stressed
Some signs that your cory catfish may be stressed or insecure when kept in too small of numbers include:
Excess Hiding
Spending the majority of time hidden is a clear sign of stress. If your corys stay hidden in caves or plants they likely do not feel safe coming out.
Loss of Color
Stressed corys can lose some of their natural coloration, often looking more pale or washed out. Providing a school can help them regain color.
Lack of Activity
Corys kept in small groups may stay inactive for long periods, not interacting much with their environment or tankmates. Healthy corys should be active.
Fin Clamping
Clamped fins that are held close to the body signal a stressed, insecure fish trying not to draw attention.
Reduced Feeding
Loss of appetite from a lack of competition or other natural behaviors can occur. Corys in schools should actively seek out food.
Aggression
Nipping, fighting, or chasing tankmates can indicate competition between too few corys. Schools remove this aggression.
Tips for Keeping Cory Catfish in Schools
Get 6+ of Same Species
It’s best to keep 6 or more cory catfish of the same species, such as 6 Julii corys or 6 Panda corys. Mixing cory species can work but single species schools promote the best schooling.
Introduce School at Once
Adding all new cory catfish at the same time helps them form a school right away. Avoid adding just 1-2 new corys at a time.
Provide Hiding Spots
Offer caves, plants and other hiding spots to help replicate their natural habitat, especially for newly added schools. This promotes security.
Add Dither Fish
Including small dither fish like neon tetras can further help cory cats feel secure about swimming openly.
Provide Open Swimming Areas
Corys school more actively when provided ample open swimming space. Avoid heavily clogged areas and provide sandy bottomed areas.
Selecting Cory Catfish Tankmates
Here are some ideal tankmates for cory catfish that school together:
Other Small Catfish
Other small, peaceful bottom-dwelling catfish like otocinclus can make good tankmates. Avoid aggressive catfish.
Small Tetras
Tetras like neon tetras, cardinal tetras, rummynose tetras etc do well with cory schools. Their activity levels match well.
Danios
Schooling danios like zebra danios are active and generally ignore corys at the bottom. They serve as good dither fish.
Rasboras
Small rasboras work well with corys but avoid fin-nipping species. Ember tetras, chili rasboras are good options.
Platies/Swordtails
Peaceful community livebearers provide activity at the middle/top levels and largely ignore corys schooling below.
Dwarf Cichlids
Some dwarf cichlids can work well, including German blue rams and apistogramma. Avoid aggressive species.
Invertebrates
Snails, shrimp, and other inverts are fine with cory schools. Avoid crayfish that may pinch corys.
Avoid Fin Nippers
Steer clear of barbs, bettas, gouramis that may nip fins of cory catfish, especially active schooling corys.
Cory Catfish Schooling Species
Here is an overview of some popular cory catfish species well suited for schooling together:
Bronze Corydoras
One of the most popular cory catfish, bronze corys are hardy and readily school in groups. They get along well in schools of 6+.
Albino Corydoras
Albino corys lack pigment but are otherwise normal corys that actively school together in groups of 6 or more.
Panda Corydoras
Panda corys have bold black and white markings. They are active schoolers that readily form groups of 6+.
Julii Corydoras
Julii corys have a pattern of pepper spots on their heads. They are active and school well in larger groups.
Sterbai Corydoras
Sterbai corys have brown bands on a pinkish body and school well together when kept in numbers.
Peppered Corydoras
Peppered corys have black spots over a gray/white body and actively school in groups of 6+.
Schwartz/Black Corydoras
All black in color, Schwartz corys school well in large groups together in the home aquarium.
Green Corydoras
Bright green corys are active but also retreat often to planted areas. They school in groups of 6+.
Habrosus Corydoras
Salt and pepper corys are active schoolers that live primarily in the lower levels of the tank.
Schooling vs Shoaling Behavior
Corydoras catfish exhibit schooling and shoaling behaviors:
Schooling
Corys actively swim together in synchronized movements as a group, turning and moving in unison as a unit. Tightly knit schools form with 6+ corys.
Shoaling
Shoaling is loosely grouping together while not necessarily swimming in synchronized patterns. Corys shoal when resting or feeding but don’t move as a unit.
Cory Catfish Water Parameters
Cory catfish should be kept in stable, clean water conditions for healthy schooling:
| Parameter | Value |
|---|---|
| Temperature | 72°F – 80°F (22°C – 27°C) |
| pH | 6.5 – 7.5 |
| Hardness | 2 – 12 dGH |
| Ammonia/Nitrite | 0 ppm |
Notes
– Softer, more acidic water is preferred, similar to their natural habitat
– Consistent water quality promotes healthy schools
– Avoid ammonia and nitrite spikes which can stress corys
Cory Catfish Tank Size
Cory catfish schooling groups should be kept in a suitably sized aquarium:
Minimum Tank Size
– 10 gallons for first 6 cory catfish
– An additional 10-15 gallons for each extra cory added
Recommended Tank Size
– 20 gallon tank for a school of 6 corys
– 30-40 gallon tank for larger schools of 10+
Aquascape Considerations
– Leave plenty of open swimming space
– Include smooth substrate like sand or fine gravel
– Heavily planted areas provide refuge but avoid overcrowding plants
Feeding Cory Catfish Schools
Proper nutrition helps promote healthy cory catfish schools:
High Quality Foods
– Sinking algae wafers, pellets for bottom feeders
– Freeze dried foods like brine shrimp, bloodworms
– Occasional blanched vegetables
Feed Small Portions
– Feed several small meals per day
– Allow 2-3 minutes for food to be consumed
– Remove any uneaten food to avoid fouling water
Supplement Diet
– Include natural foods like live or frozen brine shrimp
– Allow access to algae in planted tanks
– Provide sinking carnivore pellets to support school
Conclusion
In summary, while 2 cory catfish may get along, it is strongly recommended to keep corys in larger schools of 6 or more fish. This allows them to properly exhibit schooling and shoaling behaviors seen in the wild. Schools help reduce stress, increase activity, and promote growth and health. Providing the right tank conditions and diet also supports a thriving cory catfish school in the home aquarium!
