Yes, molly fish and cory catfish can exist in the same aquatic space without fighting one another or contracting nasty diseases.
A molly fish’s relationship with salt may create challenges. However, that particular consideration is more nuanced than people think. Mollies can survive without salt.
The guide below will also show that salt is not necessarily a death sentence for cory catfish.
Can I Keep Molly Fish And Cory Catfish Together In The Same Tank?
Yes, you can. Co-existence is only impossible when two species require wildly different parameters and conditions. That is not the case here.
First of all, their sizes are similar. Molly fish are three to five inches long. Cory catfish are one to four inches long.
The average molly fish is larger than the conventional cory catfish. But the size difference is not significant enough for the molly fish to mistake the cory catfish for food.
Secondly, both fish inhabit similar environments in the wild.
As such, they will thrive in the same aquarium if the tank is clean and they have sufficient food. Fish tend to misbehave when you restrict their access to food.
Also Read: 19 Great Molly Fish Tank Mates
Molly Fish vs. Cory Catfish: Natural Behavior
Aggression is a dangerous attribute among fish because they have nowhere to go.
If one species manifests violent tendencies, it will bully weaker neighbors until they succumb to injuries.
Therefore, you must separate aggressive fish from their peaceful counterparts. Otherwise, you risk losing the entire tank.
Fortunately, Molly fish and Cory catfish are equally friendly.
This works in the cory catfish’s favor because mollies are usually bigger. The last thing you want is a larger fish with an aggressive personality.
Molly Fish: Natural Behavior
Molly fish are a common sight in community aquariums because they get along with fish from other species. Keep them happy by placing them in groups.
A school of fish creates a sense of safety, which, in turn, keeps stress at bay.
You should endeavor to protect your fish from stress because it can incite aggression in the most peaceful species.
Cory Catfish: Natural Behavior
You can find cory catfish in sizable schools in the wild consisting of hundreds of fish.
This shows that cory catfish are social creatures that don’t mind sharing their aquatic environment with others.
Like the molly fish, schools of cory catfish are less likely to misbehave because a large group gives them a sense of security.
And even when they become a menace, cory catfish spend a lot of time searching for food at the bottom, which keeps them out of the way.
The creatures have no reason to antagonize their neighbors because they are unlikely to win a fight against the average molly fish.
Ideal Parameters For Molly Fish And Cory Catfish
| Parameters | Temperature | pH | Hardness |
| Molly Fish | 75 to 80 (F) | 7.5 to 8.5 | 12 to 25 dGH |
| Cory Catfish | 70 to 80 (F) | 6.0 to 7.0 | 5 to 10 dGH |
Molly Fish: Ideal Parameters
These are tropical fish that require warm water (75 to 80 degrees F). But you have some wiggle room.
Some molly fish types can live comfortably in 64-degree water. Talk to your retailer for additional instructions.
Most mollies don’t have unique requirements where the parameters are concerned. But if you have doubts, the retailer will clarify.
A molly fish’s origins will shape its needs. For instance, some mollies cannot live in freshwater. They prefer salt or brackish conditions.
Cory Catfish: Ideal Parameters
A cory catfish’s parameters shouldn’t concern you because they fall within the same temperature (70 – 80 F) and pH range (6.0 – 8.0) as those of a molly fish.
Try to stay within the 70 to 78 F range to keep both species happy. But again, the type matters.
Cory catfish don’t have unique requirements, but you should consult the retailer once your corys manifest an adverse reaction to the parameters in a molly fish tank.
Also Read: Mollies And Neon Tetras
Molly Fish vs. Cory Catfish: Ideal Water Conditions
| Requirements | Molly Fish | Cory Catfish |
| Ammonia | 0ppm | 0ppm |
| Nitrite | 0ppm | 0ppm |
| Nitrate | Less than 20ppm | Less than 20ppm |
| Tank Size | 20 gallons | 20 gallons |
| Foliage | Yes | Yes |
| Decorations | Yes | Yes |
| Filter | Yes | Yes |
| Heater | Yes | Yes |
| Lighting | Low – Moderate | Low – Moderate |
| Salt | Maybe | No |
Molly Fish: Ideal Water Conditions
Molly fish are not a challenge to rear. Give them stable parameters.
This means installing a heater that maintains the correct temperature range and a filtration system that matches their habits.
Mollies are messy. They eat a lot, which translates into significant volumes of waste.
Besides the filter, you must change the water weekly to control the ammonia, nitrate, and nitrite levels.
What about the salt content? This is where the problem lies. Some mollies come from salt or brackish water in the wild.
Their health may deteriorate if you move them to freshwater tanks.
Does that mean they need salt? Maybe. This debate is still ongoing. Some people add salt to their aquariums routinely to keep the mollies happy.
Others don’t add salt, and yet their mollies continue to thrive. Again, the retailer is best positioned to advise you because they know the molly’s origins.
Cory Catfish: Ideal Water Conditions
Cory catfish live in shaded regions with dense foliage in the wild. Add plants and decorations to their aquatic space.
What about the substrate? Stick to soft sand because the fish frequently search the substrate for food. A substrate with jagged edges will harm the creatures.
While the fish are adaptable, they prefer low-light environments. What about the salt? This issue is contentious. Some people argue that cory catfish are sensitive to salt.
They trap the substance, which leads to kidney failure and death. They can’t even tolerate low concentrations of salt.
Others argue that cory catfish are only sensitive to marine salt, which has minerals and elements you won’t find in aquarium salt.
The aquarium salt people use to combat diseases in freshwater fish is perfectly safe.
You will find examples that support both sides of this argument. Therefore, you are better off experimenting.
If your mollies need salt, add the cory catfish and see what happens. If their health deteriorates, move the catfish to a separate tank.
The Dietary Requirements Of Molly Fish And Cory Catfish
| Food | Molly Fish | Cory Catfish | Quantity | Schedule |
| Fish Pellets and Flakes | Yes | Yes | Small Pinch | 7 Days |
| Tubifex Worms | Yes | Yes | Small Pinch or Less | 2-3 Times Weekly |
| Bloodworms | Yes | Yes | Small Pinch or Less | 2-3 Times Weekly |
| Brine Shrimp | Yes | Yes | Small Pinch | 1 – 2 Times Weekly |
| Vegetables | Yes | Yes | Small Pinch | Twice Daily |
| Daphnia | Yes | Yes | Small Pinch | 1 – 2 Times Weekly |
| Mysis Shrimp | Yes | Yes | Small Pinch | 1 – 2 Times Weekly |
| Maggots | Yes | Yes | Fish can eat their weight in maggots | 2- 3 Times Weekly |
Molly Fish: Ideal Dietary Requirements
Mollies need the protein that live food items such as worms and shrimp offer. But they also require the nutrients found in cucumber, zucchini, lettuce, and other vegetables.
Commercial flakes and pellets can provide these nutrients. But many aquarists prefer to feed their mollies organic food.
Cory Catfish: Ideal Dietary Requirements
Cory catfish are also omnivorous. They will eat blackworms, bloodworms, algae wafers, pellets, shrimp, daphnia, and more. Try to vary their diet. Feed them once or twice a day.
Ideal Tank Size For Keeping Molly Fish And Cory Catfish
Remember that mollies and cory catfish are happiest in groups of five or more.
Therefore, 5-gallon tanks are out of the question. Ten gallons are a decent starting point, but twenty gallons are the safest.
Best Tankmates For Molly Fish And Cory Catfish
Growing only mollies and cory catfish could get a bit boring. If you have a 20-gallon tank or more, you can experiment with other species as well.
Here is a list of some peaceful types that shouldn’t pose any issues:
- Plecos
- Guppies
- Platies
- Swordtails
- Shrimp
- Snails
- Neon tetras
- Cherry Barbs
- Zebra Danios
Also Read: Can Molly Fish And Zebra Danios Live Together?
Fish To Avoid With Mollies And Cory Catfish
On the other hand, adding aggressive species should be avoided. I would vote mainly against:
- African Cichlids
- Oscars
- Arowanas
- Tiger barbs
- Rosy barbs
- Zebra danios
- Red-tailed catfish
Conclusions
For those of you in a hurry, here is a quick summary of what I discussed earlier:
- Molly fish and Cory catfish can coexist peacefully in the same tank without fighting or contracting diseases, as they have similar sizes and inhabit similar environments.
- Molly fish can survive without salt, and the consideration of salt for their well-being is more nuanced than commonly thought.
- Cory catfish are social creatures that can live in sizable schools and don’t mind sharing their aquatic environment with other species.
- Both Molly fish and Cory catfish exhibit friendly behavior and are unlikely to show aggression towards each other or their tankmates.
- The ideal tank size for keeping Molly fish and Cory catfish is 20 gallons or larger, and they can be safely housed with other peaceful species like Plecos, Guppies, and Neon tetras, while aggressive species should be avoided.