Corydoras

Corydoras catfish — cories — are some of the most loved fish in the hobby. They are small, round and busy, always nosing through the sand in little groups, and now and then one darts to the surface for a gulp of air and wiggles back down.

A large family of small catfish

There are well over 150 described cory species, and many more known only by code numbers until they are formally named. They live in streams, pools and flooded forest across South America. In 2024 scientists split the big genus Corydoras into several smaller ones, so many cories now have new scientific names — but in the hobby they are all still cories. Among the most kept:

• the bronze cory, a sturdy fish with a metallic green-bronze sheen, also bred as a pink-white albino;
• the panda cory from Peru, pale with a black patch over each eye, one on the back fin and one at the base of the tail;
• the green laser cory, with a bright green-orange stripe along its side.

Armour and spines

Cories have two rows of overlapping bony plates instead of scales, and a sharp spine at the front of the back fin and each chest fin, which they lock upright when threatened. Some species have mild venom in these spines. Like otos, they can breathe air through their gut, which is why they dart to the surface; doing so now and then is normal, but constant trips mean the water is poor.

Breeding

Cory breeding is famous for the T-position: the female presses her mouth against the male's side, catches a few eggs between her chest fins, and then sticks them to the glass, a plant or a stone. A cool water change often sets it off, imitating the start of the rainy season. The adults do not guard the eggs and will eat them, so breeders often move them to a separate tank.

Keeping cories

Cories live on the bottom, so the bottom matters most: soft sand or smooth gravel that will not wear down the sensitive whiskers they use to find food. Feed sinking food that reaches them — they cannot live on what the other fish leave over. They are happiest in a group of six or more of the same species, and they get along with almost any peaceful tank mate.