Members of the South American Corydoras genus are popular freshwater aquarium catfish, and are commonly referred to as cory catfish or simply corys.
Corys typically measure around three to five centimeters in length. They are well suited to tropical freshwater community aquariums, as they get along well with other species and are not at all aggressive. It is recommended to keep Corys in groups of six or more, as they are shoaling fish. Corys are bottom feeders, so they should be offered flake foods (which do sink), sinking pellets, and supplements of live and frozen foods.
Many Corydoras species have been described by science; in addition, many variants exist. Several hundred Corydoras species are not yet classified by science, but kept by aquarists. These species are given C-Numbers, originally devised by German fishkeeping magazine DATZ. There are 131 C-Numbers currently.
Corydoras are native to the rivers of South America, and therefore most of them prefer soft, acidic water. However, they can tolerate a wide range of water conditions. They are very sensitive to aquarium salt, though. These are easy fish to keep, being (as mentioned) peaceful, small, good at cleaning up leftover foods (though their keeper should ensure that they get their own food), active, and entertaining to watch. Though most Corydoras species are nocturnal, they will usually venture out in the daytime and forage for food. These catfish love to interact with each other, and commonly play games, follow each other around the tank, and lie together in piles. Corydoras catfish are very good choices for an aquarium, and are widely kept throughout the world.