Freshwater Fish · Catfish
Bronze Corydoras
Osteogaster aenea
Social bottom-dweller for peaceful community tanksBeginner
- Lifespan
- 5-10 years
- Size
- 2.4-3 in6-7.5 cm
- Social needs
- Highly social - keep 6+ together
- Time
- Low-moderate (daily feed, weekly water changes)
- Cost
- Low
- Diet
- Omnivore (bottom-feeder)
Overview
What is this animal?
- The Bronze Corydoras is a peaceful, armoured catfish from South America and one of the most popular bottom-dwellers in the hobby.
- Hardy and long-lived, it scours the substrate and brings constant gentle activity to the lower tank.
- It was long known as Corydoras aeneus, until a 2024 revision of the corydoras group moved it to the genus Osteogaster; shops still sell it under the old name.
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- Despite a reputation as a clean-up crew, this is not a fish that survives on leftovers.
- It is a genuine community species with real social and dietary needs that keepers must meet.
Temperament
- Bronze Corydoras are sociable and peaceful, and are happiest and most active in a shoal of six or more of their own kind.
- Kept singly or in pairs they become withdrawn, whereas a proper group displays its characteristic collective foraging and resting.
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- They coexist well with most calm community fish, including tetras, rasboras, dwarf cichlids, and peaceful barbs.
- Their gentle nature means they should not be mixed with aggressive or large predatory tankmates.
A good fit for
- Beginners wanting an active bottom-dweller
- Peaceful community aquariums
- Keepers using sand substrate
- Long-term hobbyists (often 5-10 years)
Common mistakes to avoid
- Keeping fewer than 6 (they are social)
- Sharp gravel eroding their barbels
- Assuming they survive on leftovers
- Copper/salt medications they tolerate poorly
Enclosure
Minimum 20 gallons75 litres, for a group of 6
Cannot be kept alone. The minimum is 6, and the space above is for that group.
- Keep a group in a tank of at least 20 gallons75 litres that is also at least 31.5 in80 cm long, the base Seriously Fish recommends for long-term care: a standard 30-gallon115-litre tank, at 36 in91 cm, qualifies, and a 20-gallon long76-litre long tank, at 30 in76 cm, falls just short.
- Use a soft sand or smooth, rounded fine-gravel substrate to protect their delicate barbels.
- Target 72-79°F22-26°C, pH 6.0-7.5, in a fully cycled, well-oxygenated setup.
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- Provide shaded spots, plants, and driftwood for security.
- They periodically dash to the surface to gulp air, so leave an air gap beneath a tight lid.
- Sharp or coarse gravel erodes barbels and invites infection.
Supplies
Setup
- Tank and stand
- Filter
- Heater and thermometer
- Substrate, plants and decor
- Liquid test kit
- Dechlorinator and starter supplies
Ongoing
- Sinking pellets, wafers or tablets (corydoras)
- Algae or spirulina wafers (bristlenose and otocinclus)
- Frozen bloodworm, daphnia and brine shrimp (corydoras)
- Untreated aquarium driftwood (for bristlenose plecos to rasp)
- Courgette, cucumber and spinach for blanching (bristlenose and otocinclus)
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- Veg clip or a stainless veg skewer (bristlenose and otocinclus)
- Feeding tongs or a pipette for target-feeding
- Fine sand substrate for corydoras foraging
Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)
Care routine
Daily
- Check temperature and equipment
- Head-count and look everyone over
- Sinking food at lights-out
Every few days
- Top up evaporationevery 3 days
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Weekly
- Check belly profiles
- Test the water
- Water change and gravel vacuum
- Wipe the front glass only
Every few weeks
- Trim and thin the plantsevery 2 weeks
Monthly
- Check supplies and reagent dates
- Check the driftwood
- Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
- Rinse the filter media
Health review: Quarterly bottom-dweller review, every 3 months
Tools
Care in depth
Diet
Omnivore (bottom-feeder)
- Bronze Corydoras are omnivores that should be fed directly, not left to scavenge.
- Use sinking pellets, wafers, and tablets that reach the bottom, supplemented with frozen or live bloodworm, daphnia, and brine shrimp.
- Feed once or twice daily, making sure enough food sinks past faster mid-water fish so the cories actually eat.
- Slow starvation from relying on scraps is a common cause of decline; a proper sinking diet keeps them well-rounded and healthy.
Health
Signs of good health, and the common problems
- These catfish are robust but vulnerable to two husbandry faults: barbel erosion from sharp or dirty substrate, and red blotch or fin infections in poor water.
- Keeping the substrate clean and parameters stable prevents most problems.
- They are also sensitive to high nitrate and to salt and copper-based medications, so dose carefully.
- Watch barbel length, breathing rate, and skin condition, and quarantine new fish.
- With good care, individuals routinely live well beyond five years.
Is this urgent?
6 warning signs and how fast to act, 3 of them right away
In a fish tank the patient is usually the water. Test before you treat: dosing a healthy tank for a disease it does not have makes things worse.
Go now
Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.
NowFish gasping at the surface with fast gill movement, or crowding the filter outflowIncrease surface movement now (gently in a betta or gourami tank, without creating a strong current), then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems. Bettas, gouramis and corydoras rise to gulp air as part of normal breathing; the warning is constant gulping, fast gill movement, or the whole group hanging at the top.
NowSudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths usually point at the water or the equipment rather than a pathogen, so rule those out first.
NowToday
Flashing: repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.
TodayWhite salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.
TodaySoon
Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.
A few daysNever add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it, and the time to find one is before you need one.
Bedding and substrate
3 safe, 4 with a caveat, 2 to avoid
Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.
Safe
Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.
safeSmooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.
safeBare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.
safeWith a caveat
Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.
with a caveatAquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.
with a caveatVery deep sand bedsAnaerobic pockets form below about 2 inches5 cm in still sand. Either keep it shallow or keep it stirred.
with a caveatPainted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.
with a caveatNever
Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.
neverAnything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.
neverThis is our general list for freshwater fish. We have not built one specific to Catfish yet.
Top resources for more info
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YouTubers
Girl Talks FishCare how-tos by fish type, tank setup and beginner mistakes (the host works for Aquarium Co-Op, a retailer)Aquarium Co-OpSpecies care guides, filtration and fish health (run by a retailer)Prime Time AquaticsSpecies profiles, stocking and water chemistry explained plainly
Sites
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