Catfish

• 1. Introduction

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  A Mekong giant catfish caught in northern Thailand on the 1st of May 2005 weighed 293 kilograms. The press only heard about it almost two months later. Thai officials began keeping records of such catches in 1981, and no Mekong giant on those records has been heavier. Catfish, the order Siluriformes, take their name from prominent barbels that resemble a cat's whiskers, though not every member has them. This documentary asks what those barbels actually do for a fish. It asks why so many catfish carry weapons on their fins, and how these fish make sound at all. It also follows catfish into the kitchen, into a legal fight over a name, and into a Japanese myth about earthquakes.

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• 2. Senses and Sound

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  Up to four pairs of barbels can crowd the face of a single catfish. They are the nasal pair, the maxillary pair on each side of the mouth, and two pairs under the chin called the internal and external mandibular barbels. Many families carry fewer, and some have only extremely reduced maxillary barbels.

  In most bony fish the maxilla is a tooth-bearing bone that helps the mouth push forward for suction feeding. Catfish shrank theirs into a support for the maxillary barbels. As a result, they cannot protrude their mouths the way carp do. A severed barbel grows back over time, but a maxillary barbel cannot regenerate if the maxilla itself is lost.

  Many larger catfish have chemoreceptors across their entire bodies, especially along the barbels. That means they taste anything they touch and smell chemicals in the water. In the words of one description of their senses, "In catfish, gustation plays a primary role in the orientation and location of food". Eyes matter less to such a fish, so they are generally small. Many species lost them entirely after moving into underground environments and becoming cavefish. The retinae that remain hold single cones and large rods, and many catfish add a tapetum lucidum that may help them catch scarce light.

  A Weberian apparatus, shared with other ostariophysans, joins with the reduced gas bladder to sharpen a catfish's hearing and its sound production. The fish can judge how far away a sound began and from which direction it came. Their sounds fall into two groups. For drumming, sonic muscles pull on an elastic spring called the ramus Mulleri, which stretches the swimbladder. When the muscles relax, the spring snaps the swimbladder back and the chamber resonates.

  Stridulation works more like a comb. The first ray of the pectoral fin has ridges at its base, and it normally slides in a groove on the pelvic girdle. Pressing the ridges against that groove produces a series of short, sharp taps.

  During courtship in three species of Corydoras, every male stridulated before the eggs were fertilized, and each species' song differed in pulse number and duration. A study by Maria Clara Amorim found family-specific and species-specific vocal patterns. Kaatz examined 83 species from 14 families and concluded that catfish stridulate more when disturbed and use swimbladder sounds more in conflicts within their own species. Among long-whiskered catfish, drumming is a threat and stridulation is a defense signal. The same pectoral spines that rasp out a defensive call also serve as weapons.

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• 3. Armor, Spines, and Venom

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  Most catfish sink rather than float, because of a reduced gas bladder and a heavy, bony head. Their bodies are typically cylindrical with a flattened underside, which suits feeding along the bottom. A flattened head helps them dig through sediment. Some have mouths that expand to a large size and contain no incisor-like teeth, so they feed by suction or gulping rather than biting. In the families Loricariidae and Astroblepidae, a suckermouth lets the fish fasten onto objects in fast-moving water.

  No catfish has scales. The skin is either smooth or armored with bony plates called scutes. In some species the mucus-covered skin also lets the fish breathe, in a process called cutaneous respiration. The armor takes several forms. In the loricarioids, the suckermouth armored catfishes, and in the Asian genus Sisor, it is mostly rows of free dermal plates. In the subfamily Doumeinae and in the hoplomyzontines, expanded vertebral processes form the plates instead.

  Every catfish except the electric catfishes of the family Malapteruridae has a strong, hollow, bony spine at the front of its dorsal and pectoral fins. A fish can lock these spines outward as a defense, and they can inflict severe wounds. In numerous species the spines also deliver a stinging protein made by glandular cells in the skin covering them.

  As many as half of all catfish species may be venomous this way. That makes Siluriformes overwhelmingly the vertebrate order with the most venomous species. In the family Plotosidae and the genus Heteropneustes, the venom is potent enough to hospitalize a person who is stung. The stings of Plotosus lineatus can be lethal.

  Biologists have long used these spines to sort catfish into groups and trace their relationships. The effort has struggled because no one agreed on the names for the parts. In 2022, researchers proposed a general standard for describing catfish spine anatomy to settle the problem.

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• 4. Giants and Dwarfs

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  Under 12 centimetres is the maximum length of many catfish. Some of the smallest species in the families Aspredinidae and Trichomycteridae reach sexual maturity at just 1 centimetre. The tiny ectoparasitic candiru sits at this end of the scale. At the other end stand the three largest living species: the Mekong giant catfish, the wels catfish of Eurasia, and the piraíba of South America. Few single orders of bony fish span a wider range of sizes.

  The wels catfish, Silurus glanis, ranges across Europe. Only one other catfish is native to the continent, Aristotle's catfish, which is restricted to Greece. Mythology and literature describe wels of astounding proportions that science has never verified. Fish longer than 2 metres are rare, though wels are known to exceed 2.5 metres and 100 kilograms. In July 2009, an 11-year-old British schoolgirl caught an 88-kilogram catfish in the River Ebro in Spain.

  North American records are smaller. A blue catfish, Ictalurus furcatus, taken from the Missouri River on the 20th of July 2010 weighed 59 kilograms. The largest flathead catfish ever caught, from Independence, Kansas, weighed 56 kilograms. Ken Paulie landed a flathead of 55.79 kilograms in the Elk City Reservoir in Kansas on the 19th of May 1998, and the International Game Fish Association certified it.

  In Asia, Jeremy Wade caught a 75.5-kilogram goonch on the Kali River, on the India-Nepal border, after three fatal attacks on humans. He believed the guilty fish must have been significantly larger. It had taken an 18-year-old boy as well as a water buffalo.

  The piraíba, Brachyplatystoma filamentosum, is a goliath catfish native to the Amazon Basin. It can occasionally reach 200 kilograms, as numerous catches show. Deaths from being swallowed by these fish have been reported in the region. All of these giants belong to one order whose family tree is still being redrawn.

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• 5. A Crowded Family Tree

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  About 3,093 extant catfish species have been described, grouped into roughly thirty-six families. That makes the order the second or third most diverse among vertebrates. One out of every twenty vertebrate species is a catfish.

  On the Lacantun river in the Mexican state of Chiapas, researchers found Lacantunia enigmatica in 2005 and named the family Lacantuniidae in June of that year. It was only the third new family of fish recognized in seventy years. The coelacanth in 1938 and the megamouth shark in 1983 were the others. Between 2003 and 2005 alone, over one hundred catfish species were named, three times faster than the pace of the previous century.

  Nobody agrees on the exact number of families. Nelson, in 2006, lists Auchenoglanididae and Heteropneustidae as separate families, while the All Catfish Species Inventory folds them into other families. FishBase and the Integrated Taxonomic Information System list Parakysidae separately, but Nelson and the Inventory place it under Akysidae. A 2007 and 2008 paper left Horabagrus, Phreatobius, and Conorhynchos outside every current family.

  Molecular evidence indicates that, despite their variety, all catfish descend from one common ancestor. They sit in the superorder Ostariophysi alongside carps and minnows, characins and tetras, milkfish and beaked salmons, and the South American knifefish. Most studies divide catfish into three main lineages: the family Diplomystidae, the suborder Loricarioidei of suckermouth catfishes, and the suborder Siluroidei, which holds the rest.

  The studies disagree about which lineage branched off first. Anatomy points to the Diplomystidae. Many genetic studies instead place the Loricarioidei first, though it has been suggested that this result is an error called long branch attraction. When researchers filtered the data to reduce that bias, the Diplomystidae came out earliest, matching the anatomical evidence. Eschmeyer's Catalog of Fishes follows this order, listing the diplomystid catfishes first, in a suborder of their own.

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• 6. Deep Time and Range

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  The Late Cretaceous holds the earliest definitive catfish, found in the Americas from the Campanian to the Maastrichtian stages. They include the Andinichthyidae, Vorhisia vulpes, and possibly Arius. Catfish are believed to have originated in Gondwana, centered on South America, because the most basal living groups come from there. A possible record from the earlier Coniacian-Santonian stages in Niger is considered unreliable.

  Morocco's Kem Kem Group yielded Afrocascudo, from the Cenomanian age, which may be the earliest armored catfish known. Its describers argued that such an advanced loricariid so early implied extensive diversification before the Late Cretaceous. They reasoned that much of it happened on West Gondwana, before it split into South America and Africa. Britz and colleagues countered that it is a juvenile obaichthyid lepisosteiform, possibly Obaichthys. The original authors replied that the bones were completely ossified, so the fish could not be a juvenile.

  Other fossil families include the Andinichthyidae, spanning the Late Cretaceous to the Paleogene of South America, and the Bachmanniidae of Eocene Argentina. In North America, the Astephidae lived from the Paleocene to the Oligocene and the Hypsidoridae in the Eocene.

  Today, catfish live in inland or coastal waters on every continent except Antarctica. They are most diverse in tropical South America, Asia, and Africa, and more than half of all species live in the Americas. One family is native to North America and one to Europe. Catfish are the only ostariophysans to have entered the freshwaters of Madagascar, Australia, and New Guinea.

  Most catfish inhabit shallow, running water. Representatives of at least eight families live underground, and three of those families also inhabit caves. Phreatobius cisternarum lives in phreatic habitats beneath the surface. Numerous species of Ariidae and Plotosidae, and a few of Aspredinidae and Bagridae, live in salt water. Many Auchenipteridae are active at dusk, while most Loricariidae and Callichthyidae are active by day.

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• 7. On the Table

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  Belzoni, Mississippi, anchors the American catfish industry. About 60 percent of farm-raised catfish in the United States are grown within a 65-mile radius of the town. Channel catfish, Ictalurus punctatus, support an aquaculture industry worth $450 million a year. Mississippi, Alabama, and Arkansas host the largest producers. Catfish are easy to farm in warm climates and often sold cheaply by local grocers.

  President Ronald Reagan proclaimed National Catfish Day on the 25th of June 1987 to recognize "the value of farm-raised catfish." Channel and blue catfish are the species Americans eat most. In the United States the fish is popularly crumbed with cornmeal and fried, while in Europe it is often cooked much like carp. Central Europeans long treated it as a delicacy for feast days and holidays, and migrants from Europe and Africa carried that tradition to the American South.

  Exports of a Vietnamese shark catfish, Pangasius bocourti, drew pressure from the American catfish industry in what became known as the Catfish Dispute. In 2003 the United States Congress passed a law preventing the imported fish from being labeled as catfish. Vietnamese exporters now sell it in the United States as basa. Only fish of the family Ictaluridae may be marketed there as catfish. Trader Joe's once labeled frozen Pangasius hypophthalmus fillets as "striper", and in the United Kingdom the fish is sometimes sold as "Vietnamese river cobbler".

  In Indonesia, fried or grilled catfish is served at street stalls called warung as pecel lele, with sambal and usually nasi uduk. If the fish is lightly squashed with sambal in a stone mortar, it becomes lele penyet. Malaysians call the fish ikan keli. In Bangladesh and the Indian states of Odisha, West Bengal, and Assam, the fish, locally called magur, is a favored delicacy during the monsoons.

  Hungarian cooks make harcsapaprikás, catfish in paprika sauce, served with pasta and curd cheese. In Myanmar, catfish goes into mohinga, a noodle fish soup flavored with lemon grass and ginger. Nigerians cook it in stews, and catfish pepper soup is enjoyed throughout the nation. Opinions vary, with some food critics calling it excellent and others dismissing it as watery. Because catfish lack scales, Jewish dietary law, which requires fish to have both fins and scales, rules them out as kosher.

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• 8. Namazu and Invaders

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  Namazu is the giant catfish that Japanese Shinto mythology blames for earthquakes. In that tradition, natural phenomena are caused by kami, and other kami are associated with earthquakes too. In Kyoto the culprit is usually an eel. After the 1855 Edo earthquake, prints were made that boosted the popularity of the catfish kami, which had been known since the 16th century Otsu-e. In one catfish print, the divine white horse of Amaterasu knocks down the earthquake-causing catfish.

  There is also a large and growing ornamental fish trade in catfish. Hundreds of species are sold, and Corydoras and armored suckermouth catfish, often called plecos, are especially popular in home aquaria. Banjo catfish, talking catfish, and long-whiskered catfish are also common in the trade.

  European fisheries imported Ictalurus catfish in the hope of gaining a sporting and food resource. The European stock never reached the size of fish in their native waters, and it only added ecological pressure on native European fauna. In Florida, the voracious walking catfish became a major alien pest after being introduced in freshwater areas. The flathead catfish, Pylodictis olivaris, is likewise a North American pest in Atlantic slope drainages. Plecos of the genus Pterygoplichthys, released by aquarium keepers, now live feral in warm waters around the world.

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