Species · Catfish & bottom-dwellers
Corydoras Catfish
Corydoras spp.
The endearing armoured bottom catfish — peaceful, easy, and happiest in a group of 6+ over smooth sand. A scavenger, yes, but it still needs its own sinking food.
Difficulty: BeginnerTropical community tank✓ Fact-checked care guide
Quick facts
| Adult size | ~7 cm / 3 in (bronze cory; other Corydoras species vary) |
|---|---|
| Minimum tank | ~72 L / 19 US gal for a group — SeriouslyFish recommends an 80 × 30 cm base |
| Temperature | 21–27 °C / 70–81 °F |
| pH | 6.0–8.0 |
| Hardness | 2–15 dGH |
| Filtration & flow | Cycled, moderate filtration; smooth sand or rounded gravel is essential |
| Diet | Omnivore bottom-feeder — sinking pellets/wafers plus live/frozen; it needs its own food, not just scraps |
| Social | Highly social — keep a group of at least 6 of the same species |
| Temperament | Very peaceful |
| Lifespan | 5–10+ years |
Overview
Corydoras are the busy, endearing little armoured catfish that potter along the bottom of a community tank, sifting the substrate and occasionally dashing to the surface for a gulp of air. There are many species — the bronze cory (Corydoras aeneus) shown here is the classic hardy beginner — and they are among the most good-natured fish you can keep.
They are peaceful, easy, and long-lived, with one firm rule: they are profoundly social and must be kept in a group. A lone cory is a sad, withdrawn animal; a group of six or more is confident and constantly active.
Water & tank
Bronze corys are unfussy on chemistry — pH 6.0–8.0, 2–15 dGH, and 21–27 °C / 70–81 °F suit them (some fancy/hillstream relatives want cooler or warmer, so identify your species). As always, the tank must be cycled before they go in.
The one non-negotiable is the substrate: smooth sand or well-rounded gravel. Corys feed by rooting in the substrate with delicate barbels ("whiskers"), and sharp or dirty gravel wears those barbels down and invites infection. Give them ~72 L / 19 US gal or more (SeriouslyFish recommends an 80 × 30 cm base) with open floor space and some cover.
Feeding
Corys are often sold as a "clean-up crew", which sets them up to starve. They are omnivores that need their own food — sinking pellets, wafers, and live/frozen treats (bloodworm, daphnia) that reach the bottom.
Feed after lights-out or use sinking food so they get their share before faster mid-water fish hoover it up.
Behaviour & tankmates
One of the best community citizens there is — peaceful with everything and a great companion for small tetras, rasboras, livebearers and other calm fish.
Keep a group of at least six of the same Corydoras species (they shoal with their own kind, not mixed species). Avoid aggressive or very large tankmates, and keep the substrate soft for their barbels.
What to expect
A happy group is constantly on the move, sifting sand and resting together. Occasional dashes to the surface to gulp air are completely normal — corys can breathe air through their gut; frantic, repeated surfacing, though, points to poor water.
Myths, kindly busted
“Corys are a clean-up crew that lives off leftovers.”
They need their own sinking food. Relying on scraps slowly starves them.
“One or two corys are fine.”
They are highly social shoaling fish — keep at least six of the same species or they become stressed and reclusive.
“Any gravel is fine for the bottom.”
Sharp or coarse gravel erodes their delicate barbels and causes infections. Use smooth sand or rounded gravel.
When to act
We triage, not diagnose — but these are worth a closer look (starting with a water test):
- Worn, stubby, or missing barbels — usually a substrate/hygiene problem; move to smooth sand and improve water quality.
- Constant frantic surfacing for air (beyond the occasional normal gulp) — test the water; it often signals low oxygen or poor quality.
- Reddened patches, clamped fins, or a fish sitting apart and off its food — check water parameters and, if it persists, seek fish-savvy advice.
Sources & further reading
- SeriouslyFish — Corydoras aeneus — Adult ~75 mm SL; recommended 80 × 30 cm base (~72 L / 19 US gal); temperature 21–27 °C / 70–81 °F; pH 6.0–8.0; hardness 2–15 dGH; peaceful shoaling community catfish (keep groups).
Written & fact-checked by The Finfern Team against the sources above — kind, general guidance, not a diagnosis. If something looks wrong, test your water and, if it persists, contact a fish-savvy vet.
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