Corydoras, or Corys are some of the most fascinating bottom feeders you can add to an aquarium. They come in a wide range of colors and patterns including:
- Bronze Cory Catfish (Corydoras aenos): Primarily brown with green iridescence
- Albino Cory: These Corys are derived from the Bronze Cory. They are a creamy white color with pink eyes.
- Panda Cory Catfish: White with black spots over their eyes
- Other species have stripes, spots, and even leopard-like print patterns.
Regardless of their coloring or patterns, female Corydoras will eventually get bigger than males. Juvenile and adult females will also have a more rounded underside, while males are flatter. Both males and females have the same coloration.
Insofar as swimming habits, Corys are fast moving fish that will jump out of the water from time to time. It is very important to have a tight fitting lid on their tank.
Depending on whether Corydoras are wild caught or captive bred, it is possible to keep them in a wide range of water chemistries. When combined with the large number of colors and patterns available, it is no surprise that Corys are a popular choice among aquarium keepers.
Quick Intro to Corydoras
|Scientific Name||Corydora with many different species|
|Other Names||Armored catfish, Corys, Cory Catfish, Corydoras Catfish|
Natural Habitat, Identification, and Where to Buy
Corydoras are freshwater fish that come from several sources in South America.
Both wild and captive bred Corys prefer a tank with plenty of leaf litter and drift wood.
Beyond that, the tank conditions are somewhat different based on whether or not the fish were captured from the wild.
Since Corydoras are considered catfish, it should come as no surprise there are many species related to them.
Here are a few options for buying Corys on Amazon:
Corys that have horizontal stripes on them may also be mistaken for Otocinclus or other small sucker fish.
These fish differ significantly in temperament and water parameters needs. This article is dedicated to Corydoras.
Optimal Water Conditions For Corydoras
|Temperature||72 to 78 degrees Fahrenheit|
|Water Flow Rate||Slow|
|pH||Wild caught do best in 5.5 to 7.0. Captive bred Corys have been selectively bred to do well in 7.0 to 7.8|
|Hardness||Wild caught Corys do best in soft water. Captive bred will do fine in medium to hard water|
|Aquarium Salt Recommendations||It is best to avoid using aquarium salt with Corydoras|
|Tannin Recommendations||Ideal for wild caught Corys. You can try adding tannins to the water for captive bred Corydoras, but watch the pH carefully|
|Other Water Chemistry Needs||Nitrate sensitive, keep nitrate levels below 20 ppm. It is also best to be careful with other chemicals, including air fresheners that may dissolve into the aquarium water|
|Minimum Tank Size||10 Gallons|
|Optimal Tank Size||30 Gallons|
|Optimal Tank Shape||Long and shallow|
|Recommended Filter Type||Canister with nitrate and nitrite filter pad|
|Extra Air Flow and and How to Provide It||Use multiple airstones set to low or medium to provide gentle water circulation.|
Since Corys are more sensitive to nitrates that several other aquarium fish, it is best to test the water weekly. You may need to do emergency water changes if the tank hasn’t been properly cycled, is over stocked, doesn’t have enough plants, or you overfeed the fish.
Moving Corys into your home fish tank can be complicated. These fish may already be in the wrong water chemistry when you purchase them. As such, using a slower transfer method (like what you would use for Otocinclus) may not be of much use.
Your best option is to start off by testing the water for pH and hardness in the water the fish come in. Using a quarantine tank, do the following:
- Take some fresh water and make sure the pH and hardness match the water chemistry in the fish bag.
- Put the fish and their original water in a 2 – 3 gallon tank with a small filter. The filter should also have zeolites and nitrate/nitrite filter pads in it.
- Use an aquarium tubing siphon to drip water at a rate of one drop per second from the fresh water to the tank holding the Corys.
- Watch the fish carefully for signs of distress such as clamped fins and gill pumping. Offer some food after about 3 hours in the tank to see if they are at least interested in food. If they are, it is a very good sign.
- Once the bowl is full, give the fish about 3 – 4 days to see how well they do. During this time, they should become more active and eat well if the water chemistry is right. If the water is already acidic, move it towards neutral to see if that helps. Likewise, if the water is soft, add hardening agents. On the other hand, if the water pH is neutral, shift it towards acidic. If the water is medium to hard, add a water softener.
- During the quarantine period (about 1 month), continue to slowly adjust the water chemistry in the quarantine tank until it matches the water in the community tank. By the time you move the Corys, the two water chemistries should match. Make all water changes or additions using an aquarium tube siphon at a rate of one drop per second.
Creating the Landscape
Corys love to dig around looking for scraps of food and algae. They do best in a somewhat messy looking aquarium with plenty of leaf litter and places to hide.
|Best Plants||Fast growing plants that shed a lot of leaves. Aponogeton, Java Moss, and Peacock Moss will all work well in a Cory tank.|
|Best Decorations||Driftwood and sand|
|Decorations to Avoid||Anything sharp or rough. Since Corys will may leave the bottom of the tank several times a day, it is also best to avoid air powered toys that open and close. These are fairly small fish that can easily get trapped or injured by these kinds of decorations.|
|Maximum Size||1 inch to 4 inches, depending on species|
|Rate of Growth||Reaches maturity in about 1 year|
|Life Span||Up to 20 years in captivity|
|Temperament||Shy and peaceful|
|Preferred Tank Region||Bottom dwellers|
|Scale Thickness||Corydoras do not have scales. They have armored plates that protect them from predators. Many chemicals, including antibiotics, pesticides, and aquarium salt pass easily through the plates. Care must be taken to keep chemicals and solvents to a minimum. This includes heavy metals that may be found in tap water.|
|Gill Considerations||As with other catfish related species, Corys are also able to take in some oxygen directly from the air. Their gills are adapted to slow moving water, so it is best to avoid strong currents in the tank. If you see the fish going for the top of the tank more often than usual, check the water chemistry. You may still need to add more plants to the tank to increase oxygen levels.|
|Swimbladder Considerations||Since Corys are slim bodied fish, they usually don’t have a lot of swim bladder problems. It is still best to keep them in a more shallow tank as opposed to a deep one.|
|Fin Shape Considerations||Strong and compact|
Corydoras are schooling fish that have a very hard time living alone. They need to have at least 5 others of their own species in the tank.
Unlike many other species of fish, Corys tend to do better when there are more males in the tank than females. An ideal ratio for breeding is 2 or 3 males to one female.
Even though Corys tend to be shy, they will swim and interact peacefully with Otos, glass tetras, and other non-aggressive tank mates. As with all sucker mouthed fish, however, they may be drawn to the slime coats of other species in the tank. It is best to avoid putting Corys in tanks with larger, or more aggressive community fish.
As long as there are enough Corydoras in the tank, aggression should not be a problem. If you notice on fish consistently chasing other corys, it might help to add more Corys to the tank.
As the numbers increase, the bully may still chase other fish, or a stronger one may re-establish the social order.
When corys chase or act aggressively towards fish from another species, there may be several causes. First, the other fish might be sick or about to die. This isn’t so much aggression as the Cory is simply looking for an extra meal.
While Corys aren’t known to be territorial, congested tanks can cause problems for even the most peaceful fish. It might help to move all other species out of the tank and see if that helps curb Cory aggression.
Many animals, including fish get “hangry”. Try feeding your Corys a wider selection of foods to see if that helps the situation.
The worst thing you can do to a Cory is isolate them. These fish will quickly become depressed and will stop eating until they starve to death. You can try a partition that allows the fish to see others in the tank, but only as a last resort.
Gender, Breeding, and Reproductive Considerations
As with other fish captured wild for the aquarium trade, there is a heavy toll on wild populations. Corys can be captured in the thousands using stun guns or drugs that kill well over half before they even make it to store tanks.
Those that survive the capture and shipping may only live a few days in store tanks because they were starved during shipping.
In many cases, if a Cory lives more than a month in a home tank, it is considered a success even though their lifespan should be many years longer.
Corydoras are one of the few fish that I recommend trying to breed at the home level. If you are able to get them to breed successfully, there may be enough buyers for your fish locally as well as online.
The key to breeding healthy corys starts with parents that have good genes and good health.
Start off with more common species where you can purchase captive bred fish that are sold specifically for breeding. Later on, when you have gained experience with the process, you can try wild caught fish that have more rare patterns.
Once you notice a breeding pair in your tanks, or purchase a pair, it is important to keep them in a tank by themselves.
Choose a long tank that you can divide in half easily with a partition. Later on, when the females lay eggs, it will be much easier to control water quality for the fry without having to move the parent fish to a different tank.
When females are about to lay eggs, they will clear an area of sand to make a nest. Watch carefully for a male that stays near the female after she makes a nest. This is the pair you will need to isolate with a partition.
If you notice two or more males hanging around one female, put all the males in the partition with the female because sometimes one male cannot fertilize all the eggs. Make sure the nest is in the partition with them.
Once you see the female prepare a nest area, it will also help to put a nylon stocking over the filter inlets. This will help prevent fry from getting sucked into the filter.
It is up to you to decide if you want to speed up the spawning process. To achieve this, start off by watching the barometric pressure. You can get a digital weather station that will give you the current pressure as well as projected changes. Just before the barometric pressure falls, drop the water temperature between 5 and 10 degrees in the tank.
Depending on the species, corys may have 10 or more eggs per cycle. Once the eggs are fertilized, put the corys back in the other partition of the tank. Corys will eat their own eggs as well as the fry when they hatch.
The eggs will hatch within 6 days. Once they fry consume their yolk sack and start free swimming, you can feed them spirulina, infusorans, and fry food. As the fish grow, you can gradually introduce them to sinking pellets, vegetables, and other foods.
Contrary to popular belief, Corydoras eat a wide range of foods.
While they do enjoy grazing on algae, they also need bits of animal flesh from worms other aquatic creatures.
In the wild, they eat insect larvae, worms, and just about anything else that comes their way.
|Best Sustenance Food Type||Sinking pellets or algae wafers for catfish|
|Additional Foods for Optimal Health||Brine shrimp|
|Special Foods and Considerations for Best Color and Growth||Frozen or live foods such as blood worms, tubifex, and daphnia.|
|When and How Often to Feed Fish Based on Life Cycle||Feed fry and young fish 1 – 2 times a day. If you feed fry twice a day, be careful not to foul the water. Adults once or twice daily.|
Fry food tends to be made up of very small particles that easily break down in the water. To minimize the spread, I often use an eye dropper and just put a few drops of liquified food where I see the fry. They will come up quickly and consume the food.
For adult fish, feed just once or twice day. Every week you should also add either frozen blood worms or some other meat based food to their diet. If you notice females are beginning to get heavy with eggs, increase frozen or live foods to twice a week.
Finicky Fish Management: Wild caught corys are more inclined to be finicky or go on hunger strikes than captive bred fish. Regardless of this, use the same basic steps you would use to solve this problem in other species.
Start off by making sure the water chemistry is right. If you find nitrites, ammonia, or nitrates in the water, resolve those problems first.
Unless you know for sure whether the Corys are wild caught or captive bred, adjusting the pH and hardness can be difficult.
You can try bringing the tank water to neutral pH with soft water, and gradually shift in the opposite direction the tank was in before. Only do this if all the Corys in the same species have stopped eating. If it is just one fish not eating, look for other causes first.
If you do not have tannins or driftwood in the home aquarium, try adding some. Tannins will help curb bacteria and other pathogens. They will also give a more natural habitat feel, especially for wild caught Corys.
Look for signs of aggression from within the Cory species or from others in the tank. You may need to remove bullies, provide more hiding places for the Corys, or add more of their species to help them feel safer.
Try using live or frozen foods. Live brine shrimp work well for adult Corys as well as freeze dried blood worms.
If you can get the fish to eat, give them medicated foods used to treat internal parasites.
Corys that are about to show signs of various infections may stop eating.
Under these circumstances, internal parasites can also take advantage of a weakened fish. Using medicated food can help curb the parasites before they kill the fish. Just be sure to choose a food that is safe for Corys and catfish.
Common Diseases and How to Avoid and Treat Them
When it comes to common fish diseases, Corys will come down with Ich more than body fungus, gill flukes, or other diseases. There are no specific parasites or diseases that Corys carry.
The most common disease or cause of death in Cory catfish is nitrite poisoning. If you notice Corydoras swimming higher in the tank or moving sluggishly, they may be suffering from nitrite poisoning.
Since this can kill Corys quickly once they show symptoms, you may need to do a partial water change (around 30%) along with adding nitrate and nitrate absorbers to the filter. From there, you may need to add more plants, curb feeding, or reduce the number of fish in the tank to prevent future nitrite spikes.
How to Avoid Species Specific Diseases
Regardless of whether you have captive bred or wild corys, keeping stress levels down is very important.
Make sure the water chemistry is right, and the tank mates are peaceful.
If you are keeping wild caught fish, staying as close to their natural diet as possible may also help.
|Best Antibiotics||You can use any antibiotic that is safe for catfish or corys.|
|Treatments to Avoid||Avoid salt and antibiotics that are not safe for scale-less fish.|
|Food Recommendations When Sick||Live foods such as brine shrimp and raw vegetables if they are not eating. Once you can get them to eat, try to get in at least one or two meals of medicated pellets or fish flakes.|
|Hospital Tank or Isolation Within the Community Tank Specifics||Corys have been known to die of loneliness. Isolating them when they are sick will more than likely ensure they won’t survive. If the Cory is being harassed by fish from other species, put them in a different partition of the tank. You can also try an isolation pen within the tank if other Corys are attacking the sick fish.|
3 More Things to Know About Corydoras
- Some Corys are dyed different colors. This can impact the long term health of the fish. Be wary of unusual or bright colors.
- Corys are able to shift their eyes to look like they are winking.
- The barbels around a Corydoras mouth are easily damaged. When buying fish, look for fish that have the barbels intact.
When they are in good health, Corydoras are fascinating, lively fish that will enhance any aquarium. They are also very popular because the eat algae and are known to be peaceful fish.
Since many Corys are captured from the wild, you may want to try breeding them for sale purposes.