Catfish belong to the diverse order Siluriformes, a group of ray-finned fish found in freshwater and, occasionally, marine environments worldwide. Their most recognizable feature is the presence of barbels, whisker-like sensory organs used to locate food, especially in dark or turbid water. Unlike most other fish, all members of this order lack true scales, possessing either naked, slimy skin or an outer layer of protective bony plates known as scutes. Many species also feature a strong, sharp spine at the leading edge of their dorsal and pectoral fins, which can be locked into place as a defense mechanism.
North American Game and Food Catfish
The most common catfish species encountered in the United States and Mexico belong to the family Ictaluridae, often referred to as the North American freshwater catfishes. This family includes the three species most important to anglers and the aquaculture industry: the Channel, Blue, and Flathead catfish. The Channel Catfish (Ictalurus punctatus) is the most widely distributed and is the primary species raised commercially for food. It is distinguished by a deeply forked tail; younger fish often display dark spots across their olive-brown bodies.
The Blue Catfish (Ictalurus furcatus) is the largest of the Ictalurids, regularly exceeding 50 pounds, with specimens over 100 pounds reported. Like the channel catfish, the blue cat has a deeply forked tail, but its anal fin is noticeably longer and straighter, containing 30 to 36 rays. These fish prefer large river systems and reservoirs with clear, swift water and are sought after as trophy game fish.
The Flathead Catfish (Pylodictis olivaris) is easily identified because it is the only one of the “big three” to lack a forked tail, possessing a rounded or slightly notched tail instead. Its head is distinctly flattened, and its lower jaw protrudes beyond the upper jaw, reflecting its lifestyle as an ambush predator. Flatheads inhabit rivers and streams and are typically caught using live fish as bait, contrasting with the omnivorous feeding habits of Channel and Blue catfish.
Armored and Suckermouth Catfish (Aquarium Varieties)
A different group of catfish, popular in the aquarium trade, originate largely from South America and feature specialized physical adaptations. The family Loricariidae, commonly known as Plecos or Suckermouth Catfish, are recognized by their bodies being entirely covered in three rows of overlapping bony plates.
The unique feature of the Loricariids is their ventral suckermouth, which is adapted for grazing algae and organic matter from submerged surfaces. This specialized mouth allows them to attach firmly to objects in fast-flowing water, preventing them from being swept away. Species within this family exhibit a wide range of sizes, from small ornamental varieties to those that can exceed a meter in length.
Another common aquarium group is the family Callichthyidae, which includes the small Corydoras species, often called “Corys.” These fish are also considered armored catfish, characterized by two rows of bony plates running along the lengths of their bodies. Corydoras species are bottom-dwellers, and their small size, usually under 10 centimeters, makes them popular additions to community tanks. They possess a unique physiological mechanism that allows them to gulp air at the water’s surface and absorb oxygen through their intestines, making them tolerant of low-oxygen conditions.
Global Giants and Exotic Species
Beyond North America and the aquarium trade, the order Siluriformes contains species of immense size and unusual adaptations across the globe. The Wels Catfish (Silurus glanis), native to Europe, is one of the largest freshwater fish in the world, with reports of individuals weighing over 600 pounds. This long-bodied predator demonstrates the upper limit of catfish size in Eurasian rivers.
In Asia, the critically endangered Mekong Giant Catfish (Pangasianodon gigas) is another contender for the world’s largest freshwater fish, capable of reaching lengths of up to 3 meters and weighing over 640 pounds. Unlike most large, predatory catfish, the adult Mekong Giant Catfish is a filter-feeding herbivore that subsists primarily on algae and plankton. It is notable for the near-total absence of barbels and teeth as it matures.
The family Clariidae, which includes the Walking Catfish (Clarias batrachus), showcases an adaptation for terrestrial movement. These species possess an accessory breathing organ located above their gills, allowing them to breathe atmospheric air. This adaptation enables them to survive in stagnant water and even “walk” short distances over land using their pectoral fins to move between bodies of water.