About the species
A corydoras catfish behaves quite differently depending on how much company it has. Alone or in a pair, it often stays hidden and skittish; in a group of at least six of the same species, it actively forages across the tank floor during the day, which is also its natural behaviour in South American rivers. The genus Corydoras includes more than 170 described species, and most of what's sold in shops shares the same basic rule about numbers.
Why it has to be a group
Shoaling in this fish is not a cosmetic trait but part of its biology. In the wild, corydoras move in large groups along the riverbed, which lowers predation risk and makes foraging easier. In too small a group, the fish shows more signs of stress — less feeding, more hiding, paler colouration — so a recommended minimum group of 6 individuals applies, and more is better still.
Sensitive barbels, soft substrate
Substrate matters more here than it might seem. Corydoras carry pairs of sensitive barbels on the snout that they use to feel for food along the bottom; sharp or coarse gravel can injure them and raise the risk of infection. Soft sand or smooth, rounded gravel is recommended, regardless of the substrate's colour or grain size.
Not a bottom-of-the-tank vacuum cleaner
A common myth holds that corydoras survive purely on other fish's leftovers. In reality, faster fish higher in the water column often eat most of the food before it reaches the bottom, so a group needs its own dedicated sinking food — wafers or pellets, supplemented with frozen foods such as brine shrimp or bloodworm.
Air breathing — a safety net, not a quirk
Corydoras have supplementary intestinal air breathing and regularly dash to the surface for a gulp of air, which helps them cope with lower dissolved-oxygen water. This is entirely normal behaviour, not a sign of suffocation, and it is a different adaptation from the one gouramis use for breathing air via their labyrinth organ.
Water and temperature
A sensible range is 21–27 °C, pH 6.0–8.0, general hardness (GH) around 2–15 °dH and carbonate hardness (KH) around 2–10 °dH. Commercially bred specimens are generally far more adaptable across this wide range than wild-caught ones, though sudden shifts in water quality remain risky for the whole group.
Space for the group
For a group of six, a sensible starting point is a tank with a base of at least 80 × 30 centimetres, or roughly 75 litres. For this fish, floor area matters more than tank height, since it is a bottom-dweller that rarely swims high in the water column.
Suitable tankmates
Corydoras are peaceful and pair well with equally calm fish from the middle and upper water column — small tetras, rasboras, and dwarf shrimp. Because they occupy the tank floor, they avoid direct competition for space with most smaller, peaceful species.
Different species, similar rules
Alongside the bronze corydoras, shops often stock panda corydoras, sterbai corydoras, or julii corydoras, each with its own colour pattern. Despite the difference in looks, basic care — shoaling, soft substrate, sinking food — is very similar across most popular species; the main differences lie in each species' slightly different temperature preferences.
Caution with medication
Corydoras are generally considered more sensitive to certain fish medications, particularly copper-based treatments, which holds more broadly for scaleless catfish with bony plates instead of scales. Before using any medication it's worth checking the manufacturer's guidance on safety for catfish, and erring on a reduced dose rather than the standard rate meant for all fish in the tank.
Spawning in a home aquarium
In a well-maintained tank, corydoras can spawn without any special intervention, often after a larger water change with fresh, slightly cooler water, which mimics the rainy season in the wild. The female sticks eggs to glass, plants, or hard surfaces; if the keeper isn't planning to raise fry, the presence of other fish in a community tank usually prevents the eggs from hatching on their own.
Temperament
peaceful, shoaling, curious, quietly busy
Suitable for
beginners who want a lively, entirely non-aggressive bottom shoal
Living environment
tank from 60 l with sand and plant cover, 20–26 °C, pH 6.5–7.5
Grooming
sinking tablets in the evening; never rely on other fish leftovers alone
Pros & cons
Advantages of the species
extremely peaceful, cleans leftover food from the bottom, entertaining in a group
Things to consider
needs a sand bottom, a shoal of at least six, sensitive to nitrates
Notes
Not a cleaner in the true sense – it needs its own food. Sharp substrate wears down its barbels, the most common mistake in keeping this fish.
