Corydoras Catfish: A Species Profile for the Perfect Bottom Cleanup Crew

If there is one fish I recommend more than any other to people setting up their first community tank, it is the corydoras catfish. These little armored bottom-dwellers are endlessly charming, genuinely hardy once settled, and they bring a busy, comic energy to the lower third of the aquarium that no other fish quite matches. But "cories," as almost everyone calls them, are also widely misunderstood as a disposable cleanup crew, and that misunderstanding gets a lot of them killed.

Meet the Corydoras#

Corydoras are a large genus of small South American catfish, found across slow rivers, streams, and flooded forest margins from the Andean foothills down through the Amazon and Paraná basins. There are well over a hundred described species, plus a steady stream of undescribed "C-number" and "CW-number" fish that show up in the hobby before science catches up with them.

What they all share is a body plated in two rows of overlapping bony scutes, which is where the "armored catfish" nickname comes from. They have a downturned mouth flanked by sensitive barbels they use to taste and sift through the substrate, and most species top out somewhere between 4 and 7 cm. One of their most endearing quirks is that they periodically dash to the surface to gulp a mouthful of air, which they absorb through a modified gut. This is completely normal behavior. A cory that is constantly racing up for air, though, is often telling you the water quality has slipped.

Popular species for beginners#

Not all cories are equal in temperament or tolerance, so the entry point matters:

• Bronze and albino cory (Corydoras aeneus) — the classic, forgiving, widely available, and comfortable across a broad temperature range.
• Peppered cory (Corydoras paleatus) — hardy, cool-water tolerant, and one of the easiest to breed almost by accident.
• Panda cory (Corydoras panda) — beautiful and beginner-friendly, though a touch more sensitive to warmth and nitrate than the two above.
• Sterbai cory (Corydoras sterbai) — my go-to recommendation for warmer tanks, including community setups shared with discus.

I usually steer newcomers away from the pricier wild-caught species and the delicate dwarf types until they have a stable, cycled tank under their belt. Get comfortable with aeneus first.

Why Group Size Is Not Optional#

Here is the single most important thing to understand about cories: they are profoundly social animals, and keeping one or two of them is a quiet form of neglect. In the wild they move in shoals of dozens or hundreds. A lonely cory becomes withdrawn, spends its days hiding, and often simply stops eating well.

Keep them in groups of six or more of the same species. Six is my hard floor; when I have the room I aim for eight to ten. The difference in behavior is night and day. A proper group forages together across the open substrate in the middle of the day, engages in playful chases, and rests in companionable little piles. That confidence is the whole reason you bought them.

A note on mixing: cories will loosely school with other cory species, and a mixed tank of, say, six pandas and six sterbai looks lovely. But they shoal most tightly and breed most reliably with their own kind, so if you care about natural behavior or spawning, buy in single-species groups rather than one-of-each.

Tank Setup and Water Parameters#

Cories are hardy, but hardy is not the same as indestructible. They reward a well-maintained tank and punish a neglected one faster than most people expect.

Tank size and layout#

A group of six small cories wants a footprint of at least a standard 20-gallon "long" style tank — floor space matters far more to them than height, because that is where they live. Give them:

• Open swimming areas of clear substrate to forage across, not a floor crammed edge to edge with decor.
• Shaded retreats — driftwood, a few broad plants like Anubias or crypts, and the odd cave for when they want to rest.
• A gentle to moderate current, which they enjoy far more than dead-still water.

Water parameters#

Most commercially available cories are captive-bred and adaptable, so precise numbers matter less than stability. As general targets:

• Temperature: roughly 22–26 C for most species, with warmth-lovers like sterbai comfortable a little higher.
• pH: anywhere from about 6.5 to 7.8 is fine for tank-raised stock.
• Ammonia and nitrite: zero, always. Cories should never be used to cycle a tank.
• Nitrate: keep it low with regular water changes; bottom-dwellers sit in the worst of it.

The non-negotiable is a fully cycled, mature tank. Cories are frequently sold as janitors for brand-new setups, and that is exactly backwards. They belong in an established tank, added after it has settled.

The Substrate Question#

If you take away one practical lesson from this profile, make it this: substrate is a health issue for cories, not a decorating choice.

Those delicate barbels are constantly probing the bottom for food. On sharp, coarse, or dirty gravel, the barbels get worn down, abraded, and infected. Eroded barbels are one of the most common ailments I see in cories, and they are almost entirely a husbandry problem. A fish that has lost its barbels struggles to find food and is prone to secondary infection.

The fix is simple:

1. Use soft, rounded sand or very fine, smooth gravel. Pool-filter sand and fine aquarium sand are both excellent and let cories do their natural sifting behavior, where they take in a mouthful and eject it through the gills.
2. Keep the substrate clean. Waste and uneaten food trapped in the top layer is what actually causes barbel infections. Gentle regular vacuuming and not overstocking do more than any substrate choice alone.

I have kept cories on both sand and fine smooth gravel with healthy barbels for years, so this is not strictly "sand or death." But sand makes it easy to get right, and it lets you watch the sifting behavior that makes cories so fun. Sharp, jagged substrate makes it easy to get wrong.

Feeding: They Do Not Live on Leftovers#

The biggest myth about cories is that they will happily survive on whatever the other fish drop. They will scavenge, yes, but a diet of scraps is a slow starvation, and I have seen far too many hollow-bellied cories in tanks where the owner swore they were "cleaning up just fine."

Feed them directly, and feed food that reaches the bottom. My routine looks like this:

• Sinking pellets and wafers as the staple — quality catfish or bottom-feeder pellets that sink fast, before the mid-water fish intercept everything.
• Frozen or live foods several times a week: bloodworms, daphnia, and especially frozen or live blackworms, which cories go into a genuine frenzy over.
• The occasional blanched vegetable or algae wafer, though cories are far more carnivorous than they are algae-eaters. Do not expect them to control algae; that is not their job.

Feed after lights-out or in the dim evening if you have fast, greedy tankmates who steal the sinking food before it lands. A well-fed cory has a gently rounded belly, not a sunken one and not a bloated one.

Tankmates and Temperament#

Cories are the definition of a peaceful community fish. They ignore everyone, occupy a niche nobody else wants, and never nip or squabble. That makes them compatible with the vast majority of small, non-aggressive fish: tetras, rasboras, most peaceful gouramis, dwarf cichlids like apistogrammas, livebearers, and small peaceful loaches.

A few genuine cautions:

• Avoid large or aggressive fish that see a 5 cm catfish as a snack or a target.
• Mind the temperature overlap. Some cories, like peppered, prefer things cooler than a tropical community norm, so match the species to the tank rather than the other way around.
• Handle with care. Cories have stiff, mildly venomous pectoral and dorsal spines that can lock out and tangle in nets — and deliver a genuinely painful sting to careless hands. Use a container to move them rather than a net when you can.

A Few Honest Caveats#

I love these fish, but I owe you the trade-offs. Cories can be sensitive to salt and to certain medications, particularly some ich treatments, so read labels and dose conservatively. They are also more susceptible to poor water quality than their armored appearance suggests; that armor protects against predators, not nitrate. And while many species will spawn readily in a well-kept tank, raising the fry through their fragile first weeks is a real project, not a happy accident, so go in with the right expectations.

The Bottom Line#

Corydoras catfish are one of the best additions you can make to a peaceful freshwater community, but only if you keep them as the social, active animals they are rather than as living vacuum cleaners. Buy a group of at least six, give them soft sand and open floor space to forage, feed them properly with sinking foods, and keep the water clean and stable. Do that, and you will have a bustling, comical, long-lived little squad working the bottom of your tank for years. Treat them as an afterthought, and they will quietly fade. They ask for very little. They just do not ask for nothing.