Bronze Corydoras Care Guide

The bronze corydoras is the friendliest fish in the hobby to stock around — a hardy, peaceful, long-lived armoured catfish that spends its day sifting the bottom in a busy little group. Get two things right, sand and numbers, and it is close to bulletproof.

Bronze Corydoras at a glance

The sourced figures the welfare engine uses to judge Bronze Corydoras — the parseable key facts.

Where it comes from

Bronze corys are armoured, shoaling catfish from the soft-bottomed streams, ponds and marginal shallows of South America, ranging from Trinidad and Colombia south to the Río de la Plata. They forage face-first through soft silt and sand in aggregations of twenty or thirty, and they gulp air at the surface — an adaptation to low-oxygen marginal water, not a sign of distress. That huge wild range is why they are so forgiving: a fish that spans a continent tolerates a wide band of conditions. Their spawning is keyed to the rainy season, when an inflow of cooler water drops the temperature — the trigger keepers exploit to breed them.

Did you know?

• It breathes air through its gut: a cory dashes to the surface, gulps air and absorbs oxygen across a richly blood-supplied hind intestine, venting the spent air on the way down — surfacing many times an hour is normal.
• Bronze, green, gold-laser and albino corys are all one species — just different colour strains.
• In 2024 the biggest shake-up of the cory family in a century split one genus into seven; the bronze cory is now correctly Osteogaster aenea, though shops still use Corydoras aeneus.
• It mates in a "T-position", the female taking milt into her mouth and fertilising eggs cupped in her own pelvic fins.
• Credible reports put well-kept individuals past twenty years, making it one of the longest-lived small community fish.

Tank size — and why

Plan on about 20 US gallons for a starter group of six, and think in floor area rather than volume: these are active bottom foragers, so a longer, shallower footprint beats a tall tank every time. A 60–80 cm long base gives them room to range, and bigger groups of eight or ten want a 29-gallon or larger. Pair them naturally with a mid-water school above and the whole tank comes alive across two levels. A lid is worth fitting — corys make rapid dashes to the surface and can jump.

As a guide, a 20-gallon tank comfortably suits a starter group of about 6–8 Bronze Corydoras. As floor-dwelling shoalers they want bottom area, not water column, so a bigger group or added tankmates pushes you toward a larger footprint rather than fitting in alongside.

More on numbers by tank size: How many Bronze Corydoras in a 20-gallon tank? · How many Bronze Corydoras in a 29-gallon tank? · How many Bronze Corydoras in a 40-gallon tank?

Water parameters in practice

Corys are hardy and adaptable on chemistry — neutral, soft or moderately hard water around pH 6.5–7.5 at 22–26 °C all suits them — so the parameter that actually matters is not pH but the substrate and the cleanliness of the bottom. They are a subtropical-tolerant species that dislikes sustained high temperatures, which lower oxygen and shorten life, so resist parking them in a hot discus tank. Keep nitrate low (under about 20 ppm) with regular water changes; stable, well-oxygenated, clean water beats chasing an exact number.

Diet & feeding

Despite the pet-shop myth, corys are not a clean-up crew and will not live on another fish's leftovers — they are opportunistic benthic omnivores that need their own food delivered to the bottom. Feed sinking pellets or wafers as the staple, with small live or frozen treats — bloodworm, daphnia, brine shrimp — and feed enough that food reaches the floor before faster mid-water fish strip it. Once or twice a day, small amounts; feeding after lights-out helps a shy group get its share. Constant, busy sifting of the substrate is both how they eat and a sign of a healthy fish.

Gear & setup

The single most important setup choice is fine, smooth sand. Corys forage by diving their snouts into the substrate, and sharp or coarse gravel wears away the barbels they feed with — an eroded-barbel cory slowly starves. Smooth, rounded, scrupulously clean gravel is a distant second-best; sharp gravel is simply wrong. Add gentle, well-oxygenated flow (warm water holds less oxygen), open sand foraging lanes, and some planting, driftwood and shaded retreats for security.

Temperament & behaviour

Bronze corys are peaceful, gregarious and completely non-aggressive — no territory, no fin-nipping, no meaningful squabbling among themselves. They forage and rest in company, and will loosely shoal with other corydoras species, but it is a critical mass of their own kind they actually need. Kept in too small a group they turn shy and inactive, hiding instead of working the bottom. One quirk to know: a cory handled or netted carelessly can lock its pectoral spines erect and deliver a mild sting, so move them in a container, not bare hands.

Group & social needs

Keep a minimum of six of the same species — they are obligate shoalers, and singles or pairs become stressed, withdrawn and shorter-lived. More is better: a group of eight or ten is visibly bolder, busier and more entertaining, and there is no sexual aggression or territory to manage, so the only ceiling is floor space.

Compatible tank mates (preview)

A short, engine-cleared shortlist — the species TankStocking's welfare engine clears with Bronze Corydoras and that suit its size and temperament best. Tap any to load the pairing in the planner.

• Amano Shrimp — Peaceful temperament, similar adult size.
• Bamboo Shrimp (Wood/Fan Shrimp) — Peaceful temperament, similar adult size.
• Black Neon Tetra — Uses the midwater zone, peaceful temperament, similar adult size.

One caveat on the shrimp and snails here: engine-cleared means a size, temperament and water-needs fit — it is not a guarantee of safety. An individual Bronze Corydoras may still hunt shrimp or pick at small snails, and temperament varies from fish to fish, so add invertebrates cautiously, give them cover, and watch the first encounters.

See the full Bronze Corydoras tank mates guide →

Breeding & sexing

Bronze corys are one of the easiest egg-layers to spawn, often doing it spontaneously in a community tank — the hard part is raising the fry. To trigger a spawn, mimic the rainy season with a large (50–70%) water change a few degrees cooler than the tank, plus extra oxygenation and flow, and a ratio of about two males to each female. In the distinctive "T-position" the female clamps her mouth to the male's vent, takes in milt, fertilises a clutch of eggs held in her pelvic fins, and sticks them to glass or plants. A spawn runs to roughly 100–300 eggs that hatch in three to four days; the fry need spotless water and microfoods, and most fry losses come from ammonia off uneaten food.

Lifespan

Corys are long-lived: five to ten years is normal, an average often quoted around ten, and exceptional, well-documented individuals have passed twenty (with anecdotal claims far higher). Poorly kept fish, by contrast, manage only three or four. What shortens their life is chronic poor water quality, sharp substrate and barbel damage, sustained heat, and the stress of being kept alone or in too small a group.

Common mistakes

• Sharp gravel — the number-one avoidable cause of barbel erosion and the infection that follows. Buy sand first, or do not buy the fish.
• Buying too few. Singles and pairs are a welfare failure; keep six or more.
• Treating them as algae-eaters or a clean-up crew — they need their own sinking food, not scraps.
• A tank that is too small or too tall — corys need floor area, so a tall nano is the wrong shape.
• Keeping them too warm in a permanently tropical-hot tank, which stresses this subtropical-tolerant fish and shortens its life.
• Pouring transport water into the tank — a badly-stressed cory can release a toxin in a sealed bag, so net the fish out and discard the bag water.

Signs of trouble

• Worn-down or missing barbels — the substrate-and-hygiene warning sign; correct to sand and clean water before infection sets in.
• Bloody sores or reddened patches, especially on the belly — red blotch disease, a bacterial infection corys are prone to and that spreads within a group.
• A cory resting clamped and listless, off its food and no longer foraging — a general stress or water-quality cue.
• Frantic, repeated dashes to the surface well beyond the normal occasional air-gulp — poor water quality or low oxygen.

Is this fish right for you?

Do not buy bronze corys if you are running sharp gravel and will not switch to sand, or if you cannot house a group of at least six. Skip them for a tall nano tank with little floor area, and for a permanently hot tank. Albino, green and long-finned corys are all legitimate strains of the same fish — not dyed or deformed morphs — so there is no ethical red flag there, but mass-bred batches can carry disease, so quarantine new stock.

Bringing one home

Float the bag to match temperature and add tank water gradually, then net the fish out and discard the transport water rather than pouring it in — stressed corys can foul a sealed bag. Handle them in a cup, not bare hands, to avoid the locking pectoral spines, and settle a new group over soft sand with cover so they start foraging quickly.

Common questions

How many corydoras should I keep?

At least six of the same species, and more is better. Corys are obligate shoalers — kept singly or in pairs they turn shy, stressed and short-lived, while a group of eight or ten forages confidently and is far more active.

Do corydoras need sand?

Fine, smooth sand is strongly preferred. Corys feed by sifting the substrate with their barbels, and sharp gravel wears those barbels away, leaving the fish unable to find food. Smooth rounded gravel is a second-best; sharp gravel is not suitable.

How big a tank do bronze corydoras need?

About 20 US gallons for a group of six, sized by floor area rather than height — they are active bottom foragers, so a long, low footprint suits them, and bigger groups want a 29-gallon or larger.

Are corydoras good for beginners?

Yes — they are hardy, peaceful, long-lived and tolerant of a wide range of conditions. The two things to get right are smooth sand and a group of at least six; do that and they are one of the most forgiving community fish.

Why do my corydoras keep swimming to the surface?

It is normal. Bronze corys are air-breathers that gulp atmospheric oxygen at the surface, sometimes many times an hour, especially after feeding. Only constant, frantic gasping suggests a water-quality problem.

Sources & confidence

Sources & confidence (9 species)

These back the Bronze Corydoras figures and the previewed tank mates above. Each figure is read from the TankStocking species database (v2026.06); below is the care reference behind it and how confident we are in that data. Confidence reflects the source quality, not whether any pairing is safe. Full source list and the welfare model are on the methodology page.

• Bronze Corydoras Corydoras aeneus — Seriously Fish (seriouslyfish.com/species/corydoras-aeneus) high confidence
• Amano Shrimp Caridina multidentata — Aquarium Co-Op amano shrimp care; Aquadiction high confidence
• Bamboo Shrimp (Wood/Fan Shrimp) Atyopsis moluccensis — Aquariadise (aquariadise.com/caresheet-bamboo-shrimp-atyopsis-moluccensis) high confidence
• Black Neon Tetra Hyphessobrycon herbertaxelrodi — Seriously Fish / Aqua-Fish (Hyphessobrycon herbertaxelrodi) high confidence
• Black Phantom Tetra Hyphessobrycon megalopterus — Seriously Fish (Hyphessobrycon megalopterus) high confidence
• Bleeding Heart Tetra Hyphessobrycon erythrostigma — Seriously Fish (Hyphessobrycon erythrostigma) high confidence
• Boesemani Rainbowfish Melanotaenia boesemani — Seriously Fish; Aquarium Co-Op Boesemani guide high confidence
• Bolivian Ram Mikrogeophagus altispinosus — Seriously Fish (seriouslyfish.com/species/mikrogeophagus-altispinosus) high confidence
• Brilliant Rasbora Rasbora einthovenii — Seriously Fish (seriouslyfish.com/species/rasbora-einthovenii) high confidence

Care-guide sources (5)

This guide synthesises the references below; where they disagree, the range and the disagreement are noted in the text above. The figures in the key-facts box are read from the TankStocking species database (v2026.06). Full welfare model on the methodology page.

• FishBase — Osteogaster aenea (Corydoras aeneus) — valid name, max size 7.5 cm, parameters, IUCN Least Concern, intestinal air-breathing, fecundity
• Seriously Fish — Corydoras aeneus — synonyms, size, temperature 21–27 °C, 80×30 cm footprint, sand substrate, breeding (2M:1F, cool water change)
• Aquarium Co-Op — Cory Catfish Care Guide — group of 6+, 20 gal, smooth substrate and barbels, "not algae eaters"
• AMAZONAS Magazine — A massive revision of the genus Corydoras — 2024 Dias et al. revision; aeneus moved to Osteogaster; species-complex caveat
• Wikipedia — Bronze corydoras — ~10-year average lifespan, T-position mating, dimorphism, intestinal air-breathing

More on Bronze Corydoras

Related guides on TankStocking — each scored by the same welfare engine as the planner.

This care guide is a sourced planning reference, not veterinary advice — individual fish, filtration and maintenance all matter. Cycle the tank, test your water, and observe your fish. How TankStocking works →