"Corydoras" are generally found in smaller-sized streams, along the margins of larger rivers, in marshes, and in ponds. They are native to slow-moving and almost still (but seldom stagnant) streams and small rivers of South America, where the water is shallow and very murky. Most species are bottom-dwellers, foraging in sand, gravel or detritus. The banks and sides of the streams are covered with a dense growth of plants and this is where the corys are found. They inhabit a wide variety of water types but tend toward soft, neutral to slightly acidic or slightly alkaline pH and 5-10 degrees of hardness. They can tolerate only a small amount of salt (some species tolerate none at all) and do not inhabit environments with tidal influences. They are often seen in shoals. Most species prefer being in groups and many species are found in schools or aggregations of hundreds or even thousands of individuals, usually of a single species, but occasionally with other species mixed in. Unlike most catfishes, which are nocturnal, these species are active during the daytime. "Corydoras" are capable of breathing both water and air, often swimming to the surface to quickly ingest air before re-submerging. The frequency of this air breathing behavior increases when corys are exposed to water with low oxygen availability, allowing them to tolerate periods of aquatic hypoxia.