Catfish are a group of ray-finned fish that constitute the order Siluriformes. With around 3,000 species, they represent one of the most diverse vertebrate orders. These fish are notable for the distinctive sensory barbels around their mouths, resembling a cat’s whiskers, and hence their name.
Although these fish are believed to have originated around South America, they now have a nearly cosmopolitan distribution, occupying a wide range of habitats, from rivers, lakes, and ponds to swamps and even marine waters.
Their size varies considerably among the different species. The largest species, Mekong giant catfish (Pangasianodon gigas), which also happens to be the world’s largest freshwater fish, measures up to 9.8 ft (3 m) and weighs as much as 440 lb (200 kg). In fact, one specimen caught in northern Thailand in 2005 weighed around 646 lb (293 kg).[1]
In stark contrast, one of the smallest species, the pygmy catfish (Corydoras pygmaeus), measures only around 0.75 in (1.9 cm) for males and 1 in (2.5 cm) for females.[2] Among the medium-sized catfish are species such as the channel catfish (Ictalurus punctatus), which have an average length of 1 ft (12 in).[3]
Most catfish possess a cylindrical body with a flattened underside and a broad, flattened head that enables them to dig through the substrate. They typically have moist, scaleless skin that, in some species, helps in cutaneous respiration. However, armored catfish (family Callichthyidae) bear bony plates or scutes on their skin.
These fish are characterized by whisker-like sensory barbels located around the mouth. Depending on the species, catfish may have up to four pairs of barbels covered with chemoreceptors, which help them sense their surroundings. The nasal barbels are found near the nostrils, while the maxillary barbels are positioned on each side of the mouth. On the lower jaw, there are two additional pairs called the internal and external mandibular barbels.
All except electric catfish (family Malapteruridae) have a hollow, bony, spine-like ray on the front end of their dorsal and pectoral fins. In many species, the epidermis covering these fin spines contains glandular cells that produce a venomous protein. When the fish is threatened, the spines can pierce the skin of the predator, releasing the venom into the wound. In most species, the venom causes painful but non-lethal stings, but a few, such as the striped eel catfish (Plotosus lineatus), have fatal stings.
According to Eschmeyer’s Catalog of Fishes, all catfish are subdivided into 4 suborders and 42 families (including an uncertain incertae sedis group).
These fish are found worldwide, absent only from Greenland and Antarctica. Their highest diversity occurs in the tropical regions of South America, Asia, and Africa. North America has members of only one native family, Ictaluridae.
Europe has very few native catfish species, with the wels catfish (Silurus glanis) being the most commonly found one.
They are typically found in freshwater or brackish water environments, with a strong preference for shallow, running water. However, members of a few families, including Ariidae and Plotosidae, live exclusively in marine waters.
They are opportunistic feeders that consume a wide variety of prey. Among the major food sources are the larvae of aquatic insects, shrimps, amphipods, annelids, and small crabs. Larger species, such as the wels catfish, prey on other fish, but also consume frogs, water birds, and small mammals.[4]
A few species, such as the suckermouth catfish (Hypostomus plecostomus), are omnivorous, with algae and aquatic plants comprising a significant portion of their diet.[5]
While many species are nocturnal, driftwood catfish (family Auchenipteridae) are crepuscular, and most armored catfishes are diurnal.
As bottom feeders, they open their large, expandable mouths and feed through suction or gulping, and not biting. Since they lack cutting or biting teeth, the suction created by the mouth draws food, sediment, and water inside the mouth. Then, edible material is filtered and swallowed, while debris is expelled.
Catfish are capable of producing and detecting sounds, which play a crucial role in communication and defense. They emit two main types of sounds, drumming and stridulation.
Drumming sounds are produced by the swimbladder, which acts as a resonating chamber when specialized sonic muscles contract and relax, whereas stridulating sounds are created by the pectoral fins as their spines rub against grooves in the fish’s body. They specifically produce these sounds to ward off their predators.
The average lifespan of these fish varies with species. For instance, some species, such as Corydoras paleatus, typically live around 3 to 5 years, whereas others, like the channel catfish, usually survive 8 years.[6] Surprisingly, some northern populations of wels catfish in Europe have been estimated to be approximately 70 years old.[7]
Most catfish can survive only a few minutes to a couple of hours out of water. However, the walking catfish (Clarias batrachus) can live for up to 18 hours outside water, owing to a specialized suprabranchial organ that allows it to absorb oxygen directly from the air.
These fish typically reproduce when the water warms up in spring or early summer, reaching temperatures of around 75 to 80°F (24 to 27 °C).[8] They usually spawn once a year, though some tropical species may spawn multiple times if conditions remain favorable.
Before the eggs are laid, the breeding pair builds a nest in submerged timber, weeds, or rocks. The female then lays 3,000 to 50,000 fertilized, amber-colored eggs in the nest. The male sprays his sperm over the eggs to fertilize them externally. He often fans the eggs with his fins, facilitating the circulation of oxygen. In fact, males of the genus Arius carry fertilized eggs in their mouths until they are ready to hatch.
The eggs hatch into larvae (fry), typically in 4 to 10 days. After 4 to 10 days, the larvae swim up, start to feed, and metamorphose into juveniles. The juveniles attain sexual maturity in 2 to 3 years.
Large predatory fish, such as bass, pike, and snakeheads, feed on smaller species of catfish. In shallow waters, some fish-eating birds, such as herons, egrets, and cormorants, may prey on these fish. Additionally, large reptiles, such as crocodiles, as well as aquatic and semi-aquatic mammals, may target them.
In the scarcity of food, adult wels catfish have been found to consume eggs, larvae, and small juveniles of their own species (cannibalism).[9]
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