In addition to strong maxilla with teeth, velvet catfish also have barbels, whisker-like organs containing sensory cells and taste buds. Velvet catfish have dorsal and pectoral fins with spines, which are bony structures inside their fins. They also have softer structures called rays in their dorsal, caudal and anal fins. Adults measure from 9 inches to 1 foot in length.
Diplomystes camposensis, Diplomystes chilensis and Diplomystes nahuelbutaensis are species of velvet catfish found on the western slope of the Andes, in central and southern Chile. Diplomystes viedmensis, Diplomystes mesembrinus and Diplomystes cuyanus are found in Argentina, in Mendoza and Patagonia, and especially in the Desaguadero-Salado water system. Any velvet catfish species lives in salty or brackish waters.
In addition to being part of the genus Diplomystes and the small family Diplomystidae, velvet catfish are also members of the order Siluriformes, which include 2,500 species of catfish distributed in more than 30 families. Like other catfish, the velvet catfish is also part of the class Actinopterygii, or ray-finned fishes, and the superclass Osteichthyes, which include all bony fishes, the largest group of vertebrates.
According to the IUCN Red List of Endangered Species, velvet catfish species are decreasing and considered to be potentially threatened due to predation and habitat deterioration. The introduction of other species, such as Oncorhynchus mykiss and Salmo trutta, has increased the competition for food, thus endangering the survival of Diplomystes chilensis, a species that may be extinct.