Corydoras: Cory Catfish Size, Group Size and Tank Mates

Corydoras, sold as cory catfish or corys, are small, peaceful South American catfish that live on the bottom, travel in groups and are covered in bony armour instead of scales. Wikipedia places them in the armoured catfish family, Callichthyidae, and gives a size range of 2.5 to 12 cm in standard length.

What you will notice first in an aquarium:

• Armour plates along the flanks instead of ordinary scales
• Barbels around the mouth used to search sand and gravel for food
• Sharp fin spines, which Wikipedia describes as typically venomous
• Quick trips to the surface: corys breathe air as well as water, and Wikipedia describes them darting up to take a gulp and dropping back down. This is normal behaviour, not a sign of trouble on its own

The group is large and its naming is unsettled. Wikipedia says Corydoras was once the largest genus of Neotropical fishes, with more than 160 species, and has since been split into several genera. Many fish in the trade still carry only a C-number code: as of February 2014, 158 C-numbers had been assigned and only 32 had been matched to a scientific name.

If you have a cory and do not know which one, photograph it side-on against a plain background; the FishLens app identifies it from the picture.

Most corys stay small, but species differ by a factor of four. Wikipedia gives the genus range as 2.5 to 12 cm (1.0 to 4.7 in) standard length, which is measured without the tail fin.

Two common aquarium species as examples:

• Pygmy cory, Corydoras pygmaeus: 30 mm standard length, about 1.2 inches (Seriously Fish)
• Bronze cory, Corydoras aeneus, including the albino form: 75 mm standard length, about 3 inches (Seriously Fish)

Check the species before you plan the tank. A group of pygmies and a group of bronze corys need very different amounts of floor space.

Keep corys in a group, never alone. Wikipedia says they should be kept in groups of four to six or more, and Seriously Fish gives the same minimum of 4 to 6 for the bronze cory, describing it as a gregarious fish that needs company.

For the smallest species the advice goes up. Seriously Fish recommends buying at least 6 pygmy corys, and preferably 10 or more. It also notes that pygmies, unlike most corys, often swim in midwater rather than staying on the bottom.

In the wild, Wikipedia describes corydoras as bottom-dwellers that usually gather in groups while foraging in sand, gravel or detritus, which is why a single cory in a tank tends to hide.

Only partly. Corys pick through the substrate for food, so they find some of the flakes and pellets that other fish miss. They are not a cleaning system, and they need their own food.

What the sources say:

• Seriously Fish says bronze corys should not be expected to survive on leftovers from other fish
• Wikipedia recommends sinking pellets for corys, with live and frozen foods as supplements; Seriously Fish lists sinking dried foods, frozen bloodworm and Tubifex
• Wild corys eat bottom-dwelling insects and their larvae, worms and some plant matter (Wikipedia)

Do they create a lot of waste? We found no published figure for cory waste output. They are small fish, and what they produce depends mostly on how much food goes in. The mistake to avoid is overfeeding a tank because corys are "the clean-up crew": uneaten food still breaks down in the water, and the filter and regular water changes remain what keeps the tank clean.

Yes, in the right tank. Aqueon's betta care sheet names Corydoras catfish among suitable betta tank mates, alongside tetras, calm barbs, rasboras and livebearers, and says a betta can share a peaceful community aquarium of 15 gallons or larger.

The detail most guides skip is temperature. Aqueon says to keep a betta at 76 to 85 F. Wikipedia gives 72 to 78 F for corys. The two ranges overlap only between 76 and 78 F, so a shared tank should sit in that narrow band with a reliable heater, rather than at the warm end a betta alone would tolerate.

Species choice matters too: Seriously Fish gives the bronze cory a wider range of 21 to 27 C (about 70 to 81 F), so check the needs of the exact cory you are buying. See our betta fish page for the betta side.

Corys spend their lives nosing through the bottom, so the substrate matters more than for most fish.

• Substrate: Seriously Fish recommends fine sand, with rounded gravel as an acceptable alternative
• Water: Wikipedia gives 72 to 78 F, pH 7 to 8 and hardness of 5 to 10 degrees; Seriously Fish gives the bronze cory pH 6.0 to 8.0
• Access to the surface: leave room for them to reach the top for air
• Tank mates: Wikipedia describes corys as peaceful community fish; Seriously Fish describes the bronze cory the same way
• Handling: Seriously Fish warns the pectoral-fin spines can pierce skin and may deliver a mildly toxic secretion. Move corys with a container or a fine net and avoid grabbing them by hand. If a spine punctures your skin and the pain, swelling or redness gets worse, see a doctor

Wikipedia notes that corys breed using a distinctive courtship posture known as the "T-position".

Prices depend on the species, and the spread is wide. On 25 September 2026 the Wet Spot Tropical Fish category page listed 181 corydoras and allies, from $5.99 for bronze and albino Corydoras aeneus up to $89.99 for Corydoras hephaestus, the "Fireball cory". Shrimpy Business listed its corydoras from $12.95 to $40.00 on the same date. These are single retailer prices, not a market index.

The trade in wild fish is large: Wikipedia cites more than 8,600,000 corydoras exported from the Brazilian state of Amazonas between 2006 and 2015, about 6.06% of that state's ornamental fish exports.

Species commonly sold include panda, julii, sterbai, pygmy, bronze and albino corys. Many look alike, and a C-number fish may not have a scientific name at all. Photograph the fish side-on in clear water; the pattern on the flanks and fins and the shape of the snout are what separate most species.