Catfish

Lore & Background

Most catfish are bottom feeders. In general, they are negatively buoyant, which means that they usually sink rather than float due to a reduced gas bladder and a heavy, bony head. Catfish have a variety of body shapes, though most have a cylindrical body with a flattened ventrum to allow for benthic feeding. A flattened head allows for digging through the substrate, as well as perhaps serving as a hydrofoil. Some have a mouth that can expand to a large size and contains no incisiform teeth; catfish generally feed through suction or gulping rather than biting and cutting prey. Some families, notably the Loricariidae and Astroblepidae, have a suckermouth that allows them to fasten themselves to objects in fast-moving water. Catfish do not have scales; their bodies are often naked. In some species, their mucus-covered skin is used in cutaneous respiration. In some catfish, the skin is covered in bony plates called scutes; some form of body armor appears in various ways within the order. Juvenile catfish generally resemble and develop smoothly into their adult form without distinct juvenile specializations, though exceptions exist among ariid catfish and many pimelodids. Many larger catfish have chemoreceptors across their entire bodies (especially the barbels), which means they 'taste' anything they touch and 'smell' any chemicals in the water. Because barbels and chemoreception are more important in detecting food, their eyes are generally small, and many species lost them entirely as they adapted to underground environments, becoming cavefish. All catfish other than members of the Malapteruridae (electric catfish) possess a strong, hollow, bony, leading spine-like ray on their dorsal and pectoral fins, which can be used to deliver a stinging protein; as many as half of all catfish species may be venomous.

Reader's Guide

Catfish are of considerable commercial importance, with many larger species farmed or fished for food, such as the Pangasius (a shark catfish) and Clarias (like the walking catfish). Many smaller species, such as members of the genus Corydoras, are important in the aquarium hobby. Some species, such as plecos of the genus Pterygoplichthys, are prolific invasives due to the aquarium hobby. In the Southern United States, catfish may be known by a variety of slang names, such as 'mud cat', 'polliwogs', or 'chuckleheads', though such names are regional and unstandardized. The order Siluriformes is overwhelmingly the vertebrate order with the largest number of venomous species, with venom produced by glandular cells in the epidermal tissue covering the spines. In members of the family Plotosidae and of the genus Heteropneustes, this protein is so potent it may hospitalize humans who receive a sting; in Plotosus lineatus, the stings can be lethal. Catfish also exhibit a well-developed Weberian apparatus and reduced gas bladder, allowing for improved hearing and sound production. Sexual dimorphism is reported in about half of all families of catfish, and the anatomical organization of the testis is variable among families.

Did You Know?

• All catfish lack scales, instead possessing either smooth skin or armour-plated bodies.
• As many as half of all catfish species may be venomous, making Siluriformes the vertebrate order with the largest number of venomous species.
• Catfish have chemoreceptors across their entire bodies, especially the barbels, allowing them to 'taste' anything they touch.
• The three largest catfish species alive are the Mekong giant catfish, the wels catfish, and the piraíba.