The short answer
No — a single corydoras should never be kept alone. Cories are social shoaling catfish that depend on a group to feel secure. Keep at least 6 of the same species, and ideally more. A solitary cory becomes stressed, withdrawn and prone to illness, so if you have just one, the fix is simple: add more of its kind.
Why one cory suffers
Corydoras evolved to live in large groups over the riverbed, foraging shoulder to shoulder and darting to the surface together to gulp air. Alone, that instinct has nowhere to go. A lone cory typically hides constantly, forages half-heartedly and loses condition, and the ongoing stress leaves it vulnerable to disease. People often mistake a still, hidden cory for a calm one — in reality it’s a fish that never feels safe.
What a corydoras group needs
- 6 or more of the same species (8–10 is even better)
- Smooth sand or fine rounded gravel — sharp substrate damages their barbels
- Peaceful tankmates and some shaded resting spots
- Room to forage along the bottom
Give them numbers and the right floor and cories become one of the most entertaining, busy fish in the tank.
Before you stock
If you’re down to one cory, add more of the same species once your tank can support them — see how many corydoras to keep together and how many corydoras in a 60 litre tank. Read the full corydoras care guide, choose companions with good corydoras tankmates, and cycle any new tank via how to cycle an aquarium. The same applies to lone tetras — see can I keep one neon tetra.