Common Names: Corydoras Catfish
Scientific Name: Corydoras sp
Minimum Tank Size: 20 Gallons
Care Level: Easy
Max Size: 3 Inches
Temperature: 72-80 F
Tank Level: Bottom
Colors: Black, Tan, White
Corydoras Catfish Species Overview
It may come as a surprise that Corydoras catfish are not a species. Instead, it’s a whole genus of catfish.
Let’s look a little closer at how the Corydoras catfish fit within the whole order of catfish (Siluriformes).
Corydoras catfish are in the Callichthyidae family, into which all armored catfish fall. Around 90% of Callichthyidae are in the Corydoradinae subfamily, to which Corydoras catfish belong.
If you’re looking for cory cats for your aquarium, you have many options. The Corydoras catfish genus includes over 170 recognized species and over 100 species that don’t have scientific names yet.
The unnamed species go by “C-numbers” that Hans-Georg Evers created in 1993 for a German fishkeeping magazine.
Scientists consider Corydoras difluviatilis to be the basalmost cory. Being the “basalmost” means that it’s the most typical of the species and has the most ancestral characteristics that all cories share.
The name Corydoras comes from the Greek word kory, which means helmet, and the Greek word doras, which means skin. Armored catfish have a protective “armor,” which consists of two rows of bony plates (scutes) that cover their body length.
In addition to protective armor, they have venomous spines on their dorsal and pectoral fins for protection against larger fish.
You can tell them apart from other callichthyids because they have deeper bodies and short barbells on their upper jaw.
Corydoras also have a small, ventral mouth on the underside of their body.
The Callichthyidae family is Neotropical, meaning that they originated in neotropical areas of the Americas.
However, the Corydoras subfamily lives throughout South America. You can find them from east of the Andes to the coast of the Atlantic ocean and from Trinidad to the Rio de la Plata area in Argentina.
If you’re looking for Corydoras in the wild, you will find them in slow-moving or nearly still freshwater streams or rivers. The bottoms of these streams and rivers are usually sandy or muddy, sometimes with debris and leaves.
Many cory cats live near the sides and banks of the water in areas with dense vegetation.
Corydoras catfish are small in the catfish world. They range from 1.0 to 4.0 inches (2.5 to 10 cm).
The smallest Corydoras catfish are the dwarf Corydoras (Corydoras hastatus), which come from the Amazon River and Paraguay River in Argentina, Bolivia, and Brazil. Dwarf cories usually only reach between 1.0 and 1.4 in (2.5 to 3.5 cm).
One of the largest cory cats is the robust cory (Corydoras robustus), which reaches 3.8 in (9.5 cm).
Corydoras catfish are extremely hardy. In the wild, they only live five to seven years. In the home aquarium, they’re likely to live five to ten years. Under ideal conditions, they can live up to 20 years.
It’s easiest to sex cory cats from above. The female will be more round at the midsection than their male counterparts. Females will also usually be longer and sometimes even slightly taller than males.
In some species, the females will have larger pelvic fins and more rounded dorsal fins.
Conversely, males will be shorter, more streamlined, and sometimes slightly shorter than females.
Cory cats are mild-mannered and peaceful scavengers. They get along with other species without aggression.
Because they are timid, it’s best to keep them as a shoaling fish with four, five, or more corydoras companions.
Stress and Threats
In most cases, a cory cat’s initial reaction to a threat is simply to lay still without moving.
However, when some species feel threatened or become overly stressed, they can release toxic venom into the water, which turns the water cloudy within minutes. Not only can the venom kill the fish sharing their aquarium, but it can have suicidal effects.
Some people have reported being “stung” by a stressed cory cat. Luckily, the venom only has a mild effect on human skin. It might sting for a moment or even a few hours, but it’s not anything you need to worry about in the long term.
However, a cory cat murder/suicide incident is rare. If you keep the stress levels low, add the correct tank mates, and handle them with care, a stressed corydoras poisoning the whole tank shouldn’t be an issue.
While many catfish are nocturnal and tend to be most active at night, Corydoras are diurnal and crepuscular. So, they’re mainly active during the day and at twilight.
In fact, some species are most active at twilight since they’re less timid in dim lighting. They’re also more likely to be higher in the water column during twilight.
Location in Your Tank
Corydoras usually stay close to the bottom of the tank, either resting or hiding. In fact, it’s common not to see them much at all if they have a favorite place to hide, like inside a cave or inside tank decor.
However, if you have a lot of substrate-level hiding places in the tank, you’re likely to see them more often because more hiding places make them feel more secure.
Because cories have evolved to breathe both air and water, it’s not uncommon to see them come up to the surface for a quick breath of air. When they gulp air, they store it in their intestinal walls for later and can expel any excess.
If your cory cats are surfacing more often than usual, it’s likely a sign of high water temperatures. Studies show that cories surface more often starting at 86°F (30°C) regardless of the oxygen level in the water.
Placing cories in a tank that’s the correct size with correct water parameters and an ideal setup can help your fish live a long, happy, and healthy life.
Minimum Tank Size
As with most fish, you need one gallon of water for one inch of fish.
A lone cory needs at least a 5-gallon tank. While you can place a small cory in a one-gallon tank, one-gallon tanks aren’t ideal.
While cory cats can live alone, they seem to be much happier when they’re in a group of at least four. So, if you have four dwarf cories without any other fish, you’d need a 5-gallon tank. Meanwhile, four of the largest cories would need a 20-gallon tank.
In general, Cories are adaptable to a wide range of water parameters.
It’s essential to know what type of Corydoras you have before setting the temperature in your tank.
Corydoras come from tropical waters, so most are happy in a tank with a temperature between 74°F (23°C) and 80°F (27°C).
However, some species, like the panda Corydoras, are native to colder streams and prefer a temperature range between 68°F (20°C) and 77°F (25°C).
The ideal pH for Corydoras is between 7.0 (neutral) and 8.0 (alkaline). However, they’re not especially sensitive to water pH.
In the wild, Corydoras live in a wide range of water pHs. Since some cories come from more acidic environments, you’re not likely to have a problem if you need a lower pH for cory tankmates.
Cory cats can tolerate only a little bit of salt. However, it’s important to note that some species cannot tolerate any amount of salt.
So, species research is necessary before dosing your tank with aquarium salt or Epsom salt. Plus, regular aquarium salt may kill plants.
When you set up your tank, you should consider the needs of all the fish in your tank, including your cory cats. Providing the right environment can ensure that they live longer and stay healthier. It can even allow you to see them more often.
Corydoras have evolved to be bottom feeders with a specialized head and mouth that helps them feed in fine substrate like sand. Thus, sand is the ideal substrate for cory cats. White or beige fine silica sand is best.
It’s possible to have cory cats in a tank with a gravel substrate. However, be sure that the gravel is smooth rather than jagged. If Corydoras scrounge around in gravel with sharp edges, they can damage their barbels, sometimes leading to infection or losing the barbell altogether.
Many cories come from around the banks of rivers and streams that collect a lot of leaf litter. In a home aquarium, leaf litter can provide both food and a place to hide, especially for smaller species.
Corydoras are timid fish, so they appreciate dark places to hide to feel safe and stay stress-free.
To reduce the chance of injury, it’s a good idea to choose decorations that have smooth rather than sharp surfaces and edges.
If you choose decorations with hollow openings, be sure that any holes and spaces inside are not small enough for your cory cat to get stuck.
Some decorations that cories may enjoy include:
- Coconut shells
- Smooth and flat stone
- Hollow logs
- Artificial caves
- Decorations with hiding spaces inside
It’s not 100% necessary to have plants in your tank, but they provide happier fish and better water quality. Plants offer more places to hide and help remove carbon dioxide, ammonia, nitrates, and nitrites from fish waste.
While cories generally stay at the bottom of the tank and may root around plants looking for food, they usually don’t dig up plants. However, some species like Corydoras paleatus and Corydoras aeneus sometimes uproot carpeting plants that haven’t established themselves yet.
Your cory cats will most directly benefit from plants that provide cover at the bottom of the tank. Some good plants for Corydoras that are easy to grow and don’t require CO2 to thrive include:
- Java fern: Java fern multiplies easily, providing shade and privacy for your cory cats. Floating java ferns provide extra hiding places as they find a place to attach themselves.
- Anubias: Anubias are especially hardy and leafy, providing plenty of hiding places. Choose large-leafed species and plant them in the substrate up to their nodes.
- Moss balls: A small garden of moss balls can provide safe crevices and eaves for cories to hide.
- Guppy grass: Guppy grass is a notorious refuge for timid fish. Plant it in your substrate, fertilize it, and watch it take off throughout your tank.
- Amazon sword: Amazon sword leaves provide a lot of cover for small fish. Plant several directly in the substrate to optimize hiding spots. Keep it fertilized for best results.
- Cryptocoryne: Their low-growing, broad-spread leaves make low-stress shelters for your cory cats. Their deep roots deter uprooting if you have diggers in your tank.
- Java moss: Java moss provides excellent cover for shy fish. You can let it free-float in the tank. But, it stays together better if you tie it to tank decor to allow it to root in place.
Cories tend toward shady and dark tank areas and may hide more if you use bright aquarium lights. So, having lower lighting settings can help them feel more comfortable.
Since many cory species are crepuscular, you may notice them being more active during twilight if you use a lighting system that mimics the sun’s natural lighting cycles. In addition, these types of lighting systems also keep plants healthy.
There isn’t any single type of filtration system that’s best for cory cats. However, since some cories seem to enjoy playing and spawning in currents, many fishkeepers choose the ones that provide currents near the substrate, especially in breeding tanks.
It’s important to know what type of Corydoras you have, and its specific temperature needs before deciding if you need a heater or not.
For example, keeping a cory cat that prefers its water at a minimum of 74°F (23°C) in an unheated tank can cause stress and greatly reduce their quality of life and lifespan. Thus, it’s imperative to have a heater for species native to warm waters.
By contrast, if you have a species like a panda Corydoras that can tolerate down to 68°F (20°C, it’s fine to keep it in a cold water tank without a heater.
Corydoras are bottom feeders that search through the substrate with their snout and barbells and suck food up through their mouths.
Offering flake food to your Corydoras is usually not a good idea because the faster-moving fish that live in higher tank levels are likely to eat all of the food before it gets down to the substrate.
In their native environments, Corydoras mainly eat bottom-dwelling insects, insect larvae, a variety of worms, and some plant-based debris.
So to meet their natural feeding habits, it’s best to offer them sinking pellets. You can also supplement their diet with live and frozen food.
What foods do Corydoras like to eat the most? Their favorites include:
- Sinking catfish or bottom feeder food pellets
- Shrimp pellets
- Algae tablets
- Grindal worms
- Brine shrimp
Corydoras are more difficult to breed than some other fish types. To increase your chances of successfully breeding Corydoras, you should start out with healthy juveniles at least an inch long. They will be healthier and are easier to condition for spawning.
Conditioning for Breeding
In nature, spawning tends to happen when there are drops in barometric pressure or temperature. So, creating conditions similar to the slightly cooler weather and increased insect activity that comes before a rainstorm can help mimic natural conditions in which they breed.
To condition cory cats for spawning, you should follow these steps:
- Divide breeding trios (one female and two males) into separate fully-cycled breeding tanks (10-20 gallons) with or without substrate.
- Increase the water flow if possible.
- Feed them high-quality pellet or frozen foods.
- Do a water change, adding in slightly cooler and softer water than usual.
- Keep the water at least 3°F cooler (at least 1.7°C cooler) during the breeding process, which may take a few hours or days.
The Breeding and Egglaying Process
When cories are ready to spawn, you will usually notice that they start frantically clearing out spawning sites.
The courtship process involves the female drinking the male’s sperm. The sperm pass through her intestines and then deposit on her pelvic fins. Her eggs mix with both fresh and swallowed sperm on her pelvic fins to ensure the best chance of fertilization.
A single spawning session can result in 20 to several hundred eggs. However, they probably won’t all be fertile or survive.
The eggs are very sticky, and you will find them attached to any surface in the tank, including on the tank glass, the heater, the filter, any decorations, and plants.
Protecting the Eggs
The eggs will hatch within about six days. However, it’s necessary to take extra precautions to ensure a better chance of survival once the females lay their eggs. To protect the eggs, it would be prudent to:
- Remove the hungry parents from the tank.
- Do several daily water changes or add an anti-fungal medication like Methylene Blue to prevent fungus from killing off the eggs.
- Remove any pure white eggs that have died.
The fry get their first nourishment from eating their yolk sack and won’t be hungry until 2-3 days after hatching. Start by feeding them baby brine shrimp or powdered foods until they’re about a week old. Afterward, they can transition to crushed flakes or other crushed foods.
It’s safe to add fry to the main tank when they reach an inch long.
There are several common diseases to watch out for that may afflict your Corydoras. These include:
- Bacterial infections: Bacterial infections may cause faded colors, bloating, frayed fins, cloudy eyes, open sores, red streaks, bulging eyes, or difficulty breathing.
- Fungal infections: Fungal infections cause erratic behavior, like darting or scratching. They also might develop cotton-like growths on their mouth, skin, or eyes.
- Parasitical infections: Parasitic infections cause reduced activity, loss of appetite, mucus on their body, trouble breathing, scratching, spots, or visible worms.
- Corneybacteriosis: Symptoms of this bacterial infection include a swelling head and bulging eyes.
- Finrot: Symptoms of this bacterial infection cause ragged, frayed, or decaying fins.
- Ich: This parasitical infection results in white spots covering the body and gills.
- Red blotch disease: Corydoras are particularly susceptible to this bacterial infection. You can identify it by the red blister-like sores along the belly.
Potential Tank Mates
Cory cats get along with most non-aggressive community tank fish. Some tankmates that they will peacefully co-exist with include:
- Otocinclus catfish
- Other Corydoras catfish
Corydoras With Other Corydoras
Corydoras are happiest when they have at least four or five of their own species in the tank. In the wild, you can find cory cats shoaling in groups of hundreds or thousands of cories.
In their natural habitat, a schooling group of cory cats usually contain one species, but sometimes other species might mix into the group, too. So, it’s fine to mix cory cat species. In fact, many fishkeepers mix several corydoras species together.
Tankmates to Avoid
When it comes to which tankmates don’t work well with Corydoras catfish, it’s a matter of avoiding fish that are too aggressive for these passive fish. The fish that don’t work well with cories can cause stress, injury, and even death.
Cichlids are often too aggressive for cory cats. It’s possible for larger species like Oscars to injure or even eat them.
Barbs are another species to avoid with cories. They’re nippy, overly aggressive, and can cause too much food competition and stress for cories.
Corydoras make an excellent choice as a bottom-dwelling fish for peaceful community tanks. Providing the right environment for them can allow you to see them more, make your fish happier, and allow them to live long and healthy lives.