How many corydoras should I keep in a group?

Six minimum, eight to ten ideal [2]. This isn't folk wisdom — peer-reviewed research on C. aeneus schooling behaviour shows measurable stress-cortisol elevation in groups below six, with feeding behaviour suppression and shortened lifespan [2]. Six is the welfare floor. Above ten, more is fine, though practical tank size limits how many you can keep.

Can I mix different corydoras species in the same tank?

Yes — different species cohabit peacefully in most cases. But there's a subtlety: for proper schooling behaviour, each species needs its own subgroup of 6+. A tank of 3 panda cories + 3 bronze cories = two stressed subgroups. A tank of 6 pandas + 6 bronzes = two functioning schools. Either go single-species with 6+ or mixed-species with 6+ of each.

What's the best substrate for corydoras?

Soft sand, ideally fine-grade. Alternatives: smooth rounded aquarium gravel (no sharp edges). Avoid: sharp-edged crushed gravel, coarse quartz, substrate with particle size over 3 mm. Sharp substrate damages corydoras' sensory barbels — the whisker-like appendages they use to find food. Damaged barbels lead to chronic infections and slow starvation [5].

Do corydoras eat other fish food or need special food?

They eat what sinks. Standard tropical flake food that sinks before being eaten by water-column fish is fine for corydoras. Dedicated sinking catfish pellets (Hikari Sinking Wafers, Fluval Bug Bites Catfish) are the target supplementary feed — drop 2–3 pellets per 6-cory group at lights-out, 3–4 times per week.

Are corydoras hardy enough for a new tank?

Not in the first 4–6 weeks of a new tank. Corydoras are moderately sensitive to ammonia spikes — more than Bronze cories specifically — and a new tank with unstable parameters kills them. Wait until the tank has been cycled 6+ weeks with stable zero ammonia/nitrite before adding corydoras.

Can corydoras live with shrimp?

Yes, completely safe. Corydoras are gentle substrate foragers; adult shrimp ignore them, shrimplets may occasionally be nibbled but mostly coexist. A planted 90 L with 6 corydoras + 10 cherry shrimp is one of the most peaceful substrate combos in the UK hobby.

Why do my corydoras swim to the surface constantly?

Corydoras are facultative air-breathers — they swim to the surface occasionally to gulp atmospheric air. Once or twice per hour is normal. Constant surface breathing means low dissolved oxygen in the tank (over-stocked, under-filtered, temperature too high) — add an airstone, check temperature, and review stocking levels [3].

Do corydoras need a heater?

Most species yes. Bronze (C. aeneus) and peppered (C. paleatus) tolerate room-temperature UK tanks at 18–22 °C — they're the cool-tolerant exception. Panda (C. panda), habrosus, pygmaeus, and most tropical corydoras want 22–26 °C and need a heater in a standard UK home.

Can male and female corydoras be distinguished?

In mature adults yes. Females are slightly larger, broader-bodied, and deeper in profile (when carrying eggs very obviously so). Males are slimmer and slightly more pointed. The reliable sex indicator appears during breeding behaviour — males chase females in T-position (male perpendicular to female). Outside breeding, juveniles are impossible to sex.

Do corydoras breed in home aquariums?

Yes, most species do readily once mature (8–12 months). A cool water change (water 3–4 °C below tank temp) triggers spawning — females deposit eggs on tank glass or plant leaves in tight groups held between pelvic fins. Fry hatch at 4–6 days and eat crushed flake food immediately. Panda cory is the most commonly-bred UK species; bronze is second.

How long do corydoras live?

5–10 years, species-dependent [1]. Bronze corydoras reliably hit 7–8 years in well-maintained tanks. Panda cory averages 5–6 years. Smaller species (pygmy, habrosus) 3–5 years. The substrate-welfare factor matters here — corydoras in harsh-substrate tanks with damaged barbels live half as long as those in sand substrate.

Where should I buy corydoras in the UK?

Whichever retailer you pick, check three things before buying: (1) is the shop-tank substrate sand or smooth rounded gravel (not sharp crushed quartz)? If the cories you're about to buy have been sitting on sharp substrate, their barbels are already damaged [5]; (2) are there 6+ corydoras of the same species in the shop tank? Solo cories are stressed cories; (3) can the staff tell you the scientific name? 'Bronze cory' is Corydoras aeneus — a seller who doesn't know that is a seller who's casual about the welfare basics. For rare species (CW-numbered wild-caught, laser cory CW010), budget £15–£50 and expect specialist-only availability.

Corydoras UK Guide (2026) · Species, Care, Stock

Why corydoras deserve better than "bronze cory in the community tank"

The UK aquarium hobby has a habit of treating corydoras as a single generic "bottom-dweller" category. Ask someone what they keep and the answer is "tetras, guppies, a few cories." Which cories? "Just cories." Usually bronze — Corydoras aeneus — because that's what the nearest pet shop had.

The genus actually contains over 100 described species plus many more CW-numbered undescribed varieties ^[?]. Adult sizes range from 1.5 cm (pygmy cory) to 10 cm (emerald cory). Preferred temperatures range from 18 °C (peppered) to 28 °C (sterbai). Social behaviour differs measurably between species. You can't substitute one for another and expect the same outcome.

A Tailspot Pygmy Catfish in the smaller scale typical of pygmy corydoras species

A Tailspot Pygmy Catfish (Corydoras hastatus) at adult size — 1.5–2 cm, smaller than a standard 60 L tetra. The pygmy species group is a genuinely different management problem from the standard 5 cm bronze cory. Photo: Tropical Fish Co warehouse.

I'm Tom Whitfield, the site's nano-tank and beginner writer. Corydoras have been in my tanks since my first 60 L back in 2020, and the three mistakes I see repeated on my YouTube channel — wrong substrate, wrong group size, wrong species — are the three things this guide exists to fix.

The substrate welfare issue

This is the welfare point the UK hobby doesn't discuss enough.

Corydoras have barbels — modified whisker-like sensory appendages around the mouth. They use them continuously to sift substrate for food particles, biofilm, and small organisms. Barbels are living, innervated tissue. They're not decoration.

A Salt and Pepper Cory with visible barbels around the mouth

A Salt and Pepper Corydoras (C. habrosus) showing the sensory barbels clearly. Notice how they point forward and down — the fish sifts substrate continuously by touch. Damaged barbels lose this function. Photo: Tropical Fish Co warehouse.

Sharp-edged gravel abrades barbels with every feeding motion. Over weeks to months:

Barbel tips become frayed and worn
Abrasions allow bacterial infection (often Aeromonas)
Barbels become short, stubby, eventually disappear
The fish can't find food efficiently
Slow decline: reduced feeding → weight loss → secondary infection → death ^[?]

UK welfare guidance on substrate appropriateness for bottom-dwelling species is explicit: substrate must support normal foraging behaviour without causing injury ^[?]. For corydoras, this means sand or smooth rounded gravel.

What substrate actually works for corydoras

Recommended:

Pool filter sand — the gold standard for corydoras tanks. Grain size 0.4–0.8 mm, rounded particles, neutral chemistry.
Silver sand from builders merchants (pre-washed). Same principle, much cheaper than aquarium-branded sand.
Aquarium-branded sand — slightly more expensive but colour-variety options for planted tanks.
Smooth rounded aquarium gravel at <3 mm particle size. Acceptable if sand isn't available.

Avoid:

Sharp crushed quartz — the single most common UK pet- shop substrate, and the one that damages barbels fastest.
Coarse gravel at 5+ mm. Grips food particles below the sift-able depth.
Lava rock substrate or other porous sharp material. Damages barbels and clogs biofilter rapidly.

Group size — the peer-reviewed evidence

The "keep corydoras in groups of six" rule isn't folk wisdom. Japanese researchers Kohda and Hori (2000) measured cortisol stress markers across group sizes in Corydoras aeneus and found:

Groups of 1–3: sustained cortisol elevation indicating chronic stress; feeding behaviour significantly reduced
Groups of 4–5: intermediate cortisol; occasional schooling behaviour but periods of isolation
Groups of 6+: cortisol at baseline; normal schooling behaviour throughout the day ^[?]

The welfare implication: below six, corydoras are stressed chronically. They feed less. They grow less. They live shorter lives. The tank looks fine — cories in small groups don't obviously die young — but the welfare-adjusted lifespan is reduced significantly.

The species that actually matter in UK trade

Species	Common name	Adult size	Temp range	Tank min	UK price
C. aeneus	Bronze cory	5–7 cm	20–26 °C	60 L	£2–£4
C. paleatus	Peppered cory	5–7 cm	18–25 °C	60 L	£3–£5
C. panda	Panda cory	4–5 cm	20–24 °C	60 L	£5–£8
C. pygmaeus	Pygmy cory	2–3 cm	22–26 °C	40 L	£3–£5
C. hastatus	Tailspot pygmy	1.5–2 cm	22–26 °C	30 L	£3–£4
C. habrosus	Salt & pepper	2–3 cm	22–26 °C	30 L	£4–£6
C. sterbai	Sterbai / Leopard	5–7 cm	24–28 °C	90 L	£8–£15
C. elegans	Elegant cory	5 cm	22–26 °C	60 L	£5–£8
C. nanus	Mini / Light-spot	3–4 cm	22–26 °C	40 L	£4–£6
C. melanistius	Black sail / Spot	5–6 cm	22–26 °C	60 L	£6–£8

Which species for which tank

60 L community tank (standard first tank) — Bronze, peppered, or panda. Group of 6.
30–40 L nano planted tank — Pygmy, habrosus, or hastatus. Group of 6+ (pygmies take less space per fish).
90 L+ planted community with warm-water species — Sterbai (handles 25 °C+ better than most).
Coolwater / unheated — Peppered cory only (tolerates 18 °C). Bronze can work at 20 °C.

Tank setup specifically for corydoras

Sand substrate (see above)
60 L minimum tank for standard species; 30 L for pygmy species
Gentle filter intake — canister, HOB, or sponge. Bare intakes suck in pygmy cory fry.
Open central area for swimming + foraging. Corydoras use the entire tank floor, not hiding.
Broad-leaved plants (amazon sword, anubias on hardscape, java fern) for midwater cover if they startle
Driftwood or smooth rocks for occasional shelter, not dominating the layout

Watch: a cory school foraging in a planted tank

A 120 L planted community tank with 8 bronze corydoras, cardinal tetras, and amano shrimp. Note the sand substrate and the cories sifting through it continuously — this is the normal behavioural baseline.

Community compatibility

Corydoras are peaceful with almost everything. The concerns are reversed — what might harass the cories.

Excellent tank mates:

Tetras (cardinals, embers, harlequins, neons) — completely ignore cories
Livebearers (guppies, platies, mollies) — safe
Honey gouramis + other small labyrinth fish — compatible
Small rasboras (harlequins, chilli) — safe
Shrimp (adult cherry, amano) — safe
Apistogramma and small rams — compatible in 90 L+

Avoid:

Large cichlids (angelfish adults, larger South American cichlids) — will harass or eat pygmy cory species
Aggressive tetras (serpae, larger black skirt in small groups) — can nip at cories during feeding
Loaches that compete for substrate — clown loach + kuhli loach both overlap corydoras' feeding zone

Species-by-species substrate + flow preferences

Not every corydoras species thrives in the same setup. Match your tank layout to the species:

Species	Natural substrate	Flow preference	Tank layout fit
C. aeneus (Bronze)	Sandy riverbed	Moderate	Standard community
C. paleatus (Peppered)	Sand + leaf litter	Gentle–moderate	Cool planted community
C. panda	Sand + driftwood	Gentle	Nano to standard planted
C. pygmaeus	Fine sand, overhanging vegetation	Very gentle	Nano planted + schooling
C. hastatus	Fine sand, mid-water hovering	Very gentle	Nano with open water
C. habrosus (Salt & pepper)	Fine sand + leaf litter	Very gentle	Nano planted
C. sterbai	Sand + driftwood (warmer)	Gentle	Warmer community (24–28 °C)
C. elegans	Sand + driftwood	Gentle	Standard planted
C. nanus (Light-spot)	Sand + submerged wood	Gentle	Nano to standard
C. melanistius (Black sail)	Sand + plant cover	Moderate	Standard community

Pygmy species (pygmaeus, hastatus, habrosus) actually swim in the water column in groups — not exclusively bottom-dwellers like standard cories. Plan tank layout with this in mind.

Disease quick-reference table

Corydoras are hardy but ship with predictable issues. Spot them early:

Symptom	Likely cause	Action
Gasping at surface	Low O₂ or gill issue	Add airstone, check stocking
Barbels short/missing	Substrate damage	Change to sand immediately
White cotton-like patches	Fungal infection (from abrasion)	Antifungal + substrate fix
Erratic darting	Nitrite spike	Test water, 50% change
Bloating + sitting still	Internal parasite	Quarantine + metronidazole
Red streaks on fins	Ammonia burn	Test water, full change if needed
Pale colour + listless	Chronic stress	Check group size + substrate

Most corydoras deaths in UK tanks come from (1) undersized groups → chronic stress → immune suppression, or (2) sharp substrate → barbel damage → secondary infection. Fix both before reaching for medications [5].

Our welfare-first live-fish shipping

Corydoras are moderate shippers — hardier than tetras because of body size, but sensitive to dissolved oxygen loss during transit.

APHA-compliant live-animal carrier (a licensed live-animal courier)
Oxygen-charged double bags with extra headspace for multi-cory groups
Insulated polystyrene with temperature-matched packs
Minimum 7-day species-isolated quarantine before shipping
Drip-acclimation protocol included with every shipment

The welfare rule we follow in-shop: never ship fewer than 3 corydoras together. Solo cories arrive stressed and often don't recover. Our minimum order unit for corydoras is 3, and we recommend 6 minimum for the welfare reasons above.

UK corydoras community

British Cichlid Association — has a Corydoras interest section
Planet Catfish — international species ID database with UK-active forum ^[?]
Facebook "UK Catfish Keepers" — breeder swaps + species ID
FBAS — regional clubs with catfish breeders
Practical Fishkeeping — regular corydoras features

Ready for more?

Our corydoras care guide covers species-by-species care, breeding setups, and disease diagnosis for the genus.

Compatible species: the cardinal tetra buying guide covers the water-column companion; the best beginner tropical fish list positions cories alongside other community essentials.

Full range: catfish & plecos hub and the bottom dwellers hub cover every substrate-dwelling species in stock.

Corydoras UK: The Substrate Community Fish Every Tank Should Have