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Corydoras Catfish

Fish

The armored little bottom-cleaner that schools, snoozes, and shimmies to the surface for air!

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🤓 Did you know? Corydoras catfish can breathe atmospheric air by gulping it at the surface and absorbing oxygen through their intestine - a backup adaptation for the low-oxygen waters they evolved in. This means an occasional dash to the surface for a quick gulp of air is completely normal behavior, not a sign of a sick or distressed fish.

🗓️ The first week

The numbers a new owner needs in the first week, each from the article it links to. Rows with no link come from the encyclopedia.

Before any fish: A finished cycle reads zero ammonia and zero nitrite while still processing a dose, which is a different question from how long the tank has been running.Cycling guide →
Tank size: A 20-gallon long for a school of six standard cories; dwarf and pygmy species manage in about 10 gallons. 29 or 30 gallons is better, especially for 8 to 15.Setup guide →
Group size: Six of the same species, minimum, and more is better. A lone or paired cory hides, darts and goes off its food.Handling guide →
Temperature: 72 to 78°F covers most species in the hobby. Run a heater unless the room stays warm year-round, and hold the number steady rather than chasing a precise one.Setup guide →
Water chemistry: pH 7.0 to 7.8 for captive-bred cories, which is most of the trade. Ammonia and nitrite at zero, nitrate low through regular water changes.Setup guide →
Substrate: Soft sand, or smooth rounded gravel, about 2 inches deep. No sharp or coarse gravel, and some sharp-grained planted-tank sands are flagged unsuitable for bottom-dwellers.Setup guide →
Flow and surface: Gentle movement with calm places to rest, and clear access to the surface, since they gulp air as part of normal breathing.Setup guide →
Surface dashes: An occasional dash up for air is normal. Constant ones mean the water is short of oxygen or fouled.Enrichment guide →
Not algae eaters: The cleanup-crew reputation is wrong. Cories pick leftovers off the bottom and need sinking food of their own; algae and scraps will not keep them alive.Handling guide →
Staple food: A sinking pellet or wafer for bottom feeders, around 30 to 40% protein, with worms in the rotation: live blackworms, frozen bloodworms, Vibra Bites. Flakes get eaten higher up before they ever reach the floor.Feeding guide →
Portion: Once or twice daily, cleared in 2 to 3 minutes: one wafer per 3 to 4 fish or 2 to 3 small pellets each, cut back if food sits 20 to 30 minutes. A new cory may take up to a week to eat normally.Feeding guide →
Feeding after dark: Sinking food fed for them after lights out, if faster tankmates are taking it.Enrichment guide →
Barbel erosion: Shortened, red or missing barbels, the signature cory problem, owing as much to a dirty substrate as to grain shape. Move to soft sand, do a big water change and hold nitrate under 20 ppm; barbels can regrow over 4 to 8 weeks.Health guide →
Medication: Naked bellies make them more sensitive than most community fish: reduced doses, sometimes a half or a quarter, and no full-strength copper, malachite green or formalin. For ich, raise the temperature gradually toward 82°F with strong aeration.Health guide →
Water changes: 25 to 30% weekly from the substrate, with conditioned water at tank temperature. Test nitrate first: under 20 ppm the routine is right, past 40 ppm the next change is 50%.Aquarium Water Changes →
Budget: $3 to $8 each, and six or more is the requirement, so price the school. Roughly $150 to $215 for the equipment, then $10 to $20 a month. Aquatic vets are uncommon; keepers handle most problems through water quality.Cost guide →
Lifespan: 5 to 10 years typical, with reports of up to 15.Cost guide →
Adult size: 1 to 3 inches (2.5 to 7.5 cm), pygmy species at the low end.

🚨 Emergency card

Test the water first, then act on these today. Aquatic vets are rare, so nearly all of this is handled at home.

Barbels shortened, red, or gone
Red or bloody-looking sores on the belly and flanks: red blotch disease, water fixed plus a broad-spectrum antibiotic at half dose
Small white spots like grains of salt
Frayed or receding fins

Correct the water and treat at a reduced dose, sometimes a half or a quarter of the label amount. No full-strength copper, malachite green, or formalin.

From Common Corydoras Catfish Health Issues →

📰 Where to go next

How Much Does Corydoras Catfish Ownership Really Cost?

$3 to $8 a fish and you need six, the $150 to $215 setup, and why the substrate line matters more here than for most community fish.

Corydoras Catfish Tank Setup: Substrate Is the Detail That Actually Matters

The 20-gallon-long minimum, the substrate that decides everything, gentle flow with calm resting spots, and clear access to the surface.

Corydoras Catfish Feeding: Schedule, Diet, and Why They Stop Eating

Why the cleanup-crew reputation starves them, the sinking staple, portion by the group, and seven reasons a cory stops eating.

Corydoras Catfish Aren't Handled, and They're Not Solo Fish Either

An observation fish, the six-fish welfare floor, and why the dash to the surface is not distress.

Common Corydoras Catfish Health Issues

Barbel erosion, red blotch, ich at a reduced dose, and why this species tolerates medication worse than its tankmates.

Corydoras Enrichment: Sand for the Sifting, Not for the Barbels

What the barbel story actually rests on, the behavioral case for sand, and feeding after lights out.

🛒 What to buy

20-gallon long tank, 29 or 30 gallons preferred

Heater

Gentle-flow filter

Water test kit

Water conditioner

Soft sand, about 2 inches deep

Plants and hides for shaded cover

Sinking pellets or wafers for bottom feeders

Frozen or live worms for the rotation

Gravel vacuum

A group of six or more of one species

Prices and the reasoning behind each item are in How Much Does Corydoras Catfish Ownership Really Cost?.

❓ Frequently Asked Questions

Do corydoras catfish eat algae?

Not effectively. Left to live off leftovers and algae film as a self-sufficient cleanup crew, a cory can slowly starve, especially alongside faster, more aggressive eaters. They need dedicated sinking food, offered on purpose every time.

Does gravel wear down corydoras barbels?

That is the standard explanation, and no controlled study establishes it, or any competing mechanism. What is documented is that substrate of any kind harbors pathogenic bacteria, so a clean substrate matters more than its grain shape, and plenty of keepers have raised healthy corydoras on smooth gravel for decades.

Why are corydoras catfish more medication sensitive than other fish?

They're armored catfish with sensitive, naked bellies, and notably more medication sensitive than many community fish. That means reduced doses, sometimes a half or a quarter of the standard amount, and no full-strength copper, malachite green, or formalin, which this species tolerates poorly.

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Corydoras Catfish

Osteogaster aenea (formerly Corydoras aeneus)

Animal facts & overview