Siluriformes (Catfishes)

(vertebrate zoology) The catfishes, a distinctive order of actinopterygian fishes in the superorder Ostariophysi, distinguished by a complex Weberian apparatus that involves the fifth vertebrae and one to four pair of barbels.

(Catfishes)

Class: Actinopterygii

Order: Siluriformes

Number of families: 34

Evolution and systematics

The late nineteenth century work of Carl H. Eigenmann and Rosa Smith Eigenmann on South American catfishes established the foundation upon which later researchers, such as William A. Gosline, George S. Myers, and Mario C. C. de Pinna, have built to clarify the classification of catfishes. However, the classification is still uncertain, and there is no full agreement among the authors about the relationships of the families. Most knowledge about the phylogeny of siluriforms comes from the research on Neotropical groups carried out in the last three decades of the twentieth century.

During the International Symposium on Phylogeny and Classification of Neotropical Fishes (Porto Alegre, Brazil, July 1997), de Pinna presented a talk about the interrelationships of Neotropical catfishes. He proposed a preliminary cladistic hypothesis that accepted 12 monophyletic groups of siluriforms. In at least three cases, the relationships between New World and Old World clades are well established: the South American diplomystids, the sister group to all other catfishes; the African mochokids, the sister group to the South American doradoid superfamily, which includes the doradids and the auchenipterids; and the South American aspredinids, the sister group to the Asian erethistids. Nevertheless, de Pinna's cladogram implies the existence of four more transcontinental phylogenetic relationships. The discovery of close inter-relationships between systematic groups otherwise isolated in a continental block is relevant, due to the fact that most groups of ostariophysean fishes, such as siluriforms, primarily inhabit freshwaters.

Catfish fossils include Andinichthys, Incaichthys, and Hoff-stetterichthys (family Andinichthyidae) from the Upper Cretaceous and early late Paleocene of Bolivia; Corydoras revelatus (family Callichthyidae) from the late Paleocene of Argentina; Hypsidoris farsonensis, the only known species of the family Hypsidoridae, from the early middle Eocene of Wyoming, United States; late Eocene or early Oligocene (about 37 million years ago) material from Antarctica; Hoplosternum sp. (family Callichthyidae) from the middle Miocene of Colombia; and some material of the arioid (from the Arioida group) material from coastal marine Eocene deposits from Camden (Arkansas, United States).

It has been shown, based on cladistic grounds, that the gymnotiforms, or electric knifefishes, are the group most closely related to the siluriforms. Some authors have chosen to include both orders under the Siluriformes, a lead not followed here.

Physical characteristics

Catfishes are well known and recognized worldwide by a few characteristics. They normally show one to four pairs of barbels on the head around the mouth: one nasal, one maxillary, and two on the lower jaw or mandible. The nasal and/or lower jaw barbels may be absent, but in any case, the maxillary barbels are the longest. As these threadlike structures have plenty of taste buds, they have chemosensory and tactile functions, allowing the small-eyed catfishes to gather food efficiently.

Catfishes usually have spiny rays at the front of the dorsal and pectoral fins. These thornlike structures are large, unsegmented, and strong elements, technically similar to the other lepidotrichia, the rays that support the fins. Most families of siluriforms have two dorsal fin spines; the first is tiny, but very important, because it locks the second, larger spine in an erect position. A catfish with erected, pointed spines is nicely protected from most potential predators. The spines in some families also deliver a toxin produced in an associated venom gland. Although formidable weapons, spines are lacking in some catfish groups.

Most catfish species have a "naked" body because their leatherlike skin is completely scaleless. However, the so-called armored catfishes are covered at least partially by deeply embedded bony plates or by tubercles. Other external characteristics of catfishes are an adipose fin, usually present, sometimes rayed or preceded by a spine, and a small and toothless maxilla.

There are several internal characteristics worth mentioning, such as reductions, fusions, or absences in the set of skull bones typical of lower teleosts, as well as of intermuscular bones. The Weberian apparatus of catfishes involves five vertebrae, and their caudal skeleton is variable, ranging from six independent plates to the complete fusion of all its elements.

Distribution

Catfishes are mainly inhabitants of freshwaters, reaching their highest diversity in South America. There are more than 1,650 catfish species in South America distributed in eight monophyletic and endemic groups, including the richest family, the suckermouth armored catfishes (Loricariidae), with around 800 species. Loricariids and five other families form the armored catfishes, the largest monophyletic group of the order, with at least 1,150 species and a range between Costa Rica and Argentina. Included in this clade is the most speciose catfish genus, the plated catfishes Corydoras (Callichthyidae) with about 142 species. Other families of armored catfishes are the monotypic Nematogenyidae, the pencil or parasitic catfishes (Trichomycteridae), the spiny dwarf catfishes (Scoloplacidae), and the climbing, or South American hillstream, catfishes (Astroblepidae). The long-whiskered or antenna catfishes (Pimelodidae) used to be the second largest family, with about 300 species. However, since it is not a natural group, it was officially split in 2001 into three monophyletic families: the pimelodids (in the narrow sense), the heptapterids (Heptapteridae), and the pseudopimelodids (Pseudopimelodidae). In any case, Heptapteridae, the most species-rich group of the "old" long-whiskered catfishes with about 150 species, is widely distributed from Southern Mexico to Argentina. The remaining monophyletic groups of South American catfishes are the velvet or Patagonian catfishes (Diplomystidae), the whalelike catfishes (Cetopsidae), the doradoids (including the thorny or talking catfishes, Doradidae, and the driftwood catfishes, Auchenipteridae), and the banjo catfishes (Aspredinidae). The bullhead or North American freshwater catfishes (Ictaluridae), with 44 species, is officially the only family of the order endemic to North America, ranging as far south as Guatemala. The so-called Chiapas catfish was presented to the scientific community at the 2000 meeting of the American Society of Ichthyologists and Herpetologists; this unusual catfish seems to deserve its own family. So far, it is only known from southern Mexico.

Old World catfishes are also highly diverse; more than 1,000 species are known from Africa and Eurasia. The bagrid catfishes (Bagridae), the airbreathing or labyrinth catfishes (Clariidae), the glass catfishes (Schilbeidae), and the eeltail or tandan catfishes (Plotosidae) are the four families occurring in both Africa and Asia. Bagridae is the richest family of these widely distributed catfish clades, with about 130 species. The other three families include about 170 species. There are six catfish families endemic to Africa. Of them, the squeakers or upside-down catfishes (Mochokidae) is the richest, since it contains about 180 species; two-thirds of which are included in the genus Synodontis. The loach or African hillstream catfishes (Amphiliidae) has about 60 species. Other endemic African families are the claroteids (Claroteidae), the auchenoglanidids (Auchenoglanididae), the electric catfishes (Malapteruridae), and the austroglanidids (Austroglanididae); together these four groups contain more than 100 species.

Asia is next to South America in the number of endemic catfish families. However, these tend to be poorly speciated groups, usually with fewer than 30 species each. The sucker or Asian hillstream catfishes (Sisoridae) is the richest family, with a few more than 110 species. Other endemic Asian families are the stream or shortfin catfishes (Akysidae) with 27 species, the shark catfishes (Pangasiidae) with 26 species, the torrent or Asian loach catfishes (Amblycipitidae) with 25 species, the erethistids (Erethistidae) with 13 species, and the armorhead or Chinese catfishes (Claroglanididae) and the squarehead or frogmouth catfishes (Chacidae), both with 3 species. The sheatfishes (Siluridae) is the only family of catfishes extending its range to Europe; it includes about 100 species, only 2 of which occur in Europe.

Finally, two families have widely invaded the marine realm; interestingly, both groups include the only catfishes known from Australia. The eeltail catfishes, a rather small family of 27 species, is known from the Indian and the western Pacific Oceans and extends to Japan and Fiji. The sea catfishes (Ariidae) includes about 200 species in all the tropical continental shelves.

Habitat

Catfishes occupy practically all freshwater environments, where they are often the dominant group of fishes. Catfishes are mostly benthic and freshwater inhabitants, and they can be ubiquitous in the rivers of tropical continents such as South America and Asia, invading habitats such as riffles and waterfalls, as well as marginal, almost stagnant ponds. Some groups occupy the water column, swimming above the bottom. In those hovering catfishes some bizarre adaptations are noteworthy. Some sheatfishes and glass catfishes, for example, hover tail down, and both groups are schooling, transparent, with long barbels (one or four pairs), a long anal fin, a minute or absent adipose fin, a forked tail, and a dorsal fin completely lacking or represented by a sole reduced ray. Other catfishes, such as some banjo catfishes and most eeltail and sea catfishes, are estuarine and may venture even to deep-bottom continental-shelf environments or to offshore islands.

Behavior

Catfishes are generally bottom-dwelling, nocturnal, and solitary inhabitants of freshwater environments. However, an important minority are relatively specialized. For example, some sheatfishes, glass catfishes, and long-whiskered catfishes live far away from the bottom, are diurnally active, and may form schools. Eeltail catfishes and some thorny catfishes are well known for forming relatively large schools close to the bottom. Many South American species of armored catfishes are benthic and diurnal.

Feeding ecology and diet

Catfishes exhibit a wide array of feeding strategies. Most species live intimately linked to the bottom and feed mainly on invertebrates. Fish eaters are also abundant. For example, the squarehead, angler, and frogmouth catfishes (Chacidae) belong to a small group of Asian species that may use their maxillary barbels to attract smaller fishes to their enormous mouths. On the other hand, the Neotropical suckermouth armored catfishes (Loricariidae) are basically plant eaters, taking aquatic and terrestrial materials, such as algae and fallen leaves and trees. Catfishes, mainly those included in the pencil catfish family (Trichomycteridae), also engage in parasitic activities. Parasitic catfishes may be lepidophagous, targeting mucus, scales, and associated tissues (stegophyline trichomycterids), or hematophagous, swallowing blood (vandelliine trichomycterids). Some lepidophagous parasitic catfishes eat large pieces of flesh and enter the body cavities of their host. These species attack and devour commercially important catfishes trapped in nets or hooks and are therefore considered pests.

Catfishes are under the predatory pressure of almost all carnivores sharing their habitat. Even large predatory species are eaten as eggs, larvae, and juveniles. Their main fish predators are gars, bony tongues, trahiras, Nile perch, cichlids, and of course, other catfishes. Non-fish predators include crocodiles and caimans, and freshwater and coastal dolphins.

Reproductive biology

The usual process of catfish reproduction involves adult specimens with reduced or absent external sexual dimorphism and some courtship activity before the demersal spawning, followed by moderate engagement in parental care of the rather small eggs. Most guarding of eggs and fry is carried out by males. Nevertheless, females of some relatively large banjo catfish species, such as Aspredinichthys tibicen and Aspredo aspredo, manage to adhere the eggs after fertilization to spongy tentacles or cuplike depressions present seasonally on their bellies. It has been said that the mother nurtures the litter. Another highly derived system, brood parasitism, has been developed by a squeaker species, Synodontis multipunctatus, which could be referred to as an aquatic "cuckoo." This Lake Tanganyika mochokid shares its habitat with a mouth brooding species of Cichlidae. The catfish synchronizes its spawning activity to that of the cichlid, allowing the perciform female to ingest its eggs for mouth brooding. The process does not end when the squeaker eggs hatch. Since the squeaker eggs hatch before the cichlid eggs, the catfish fry feed upon the host's fry inside her mouth!

In many cases parental care by the male is highly significant. Perhaps the best example of this is the mouth-breeding sea catfish. Sea catfishes are relatively dimorphic: females develop pads or claspers on the pelvic fins and males shed the teeth on the roof of their mouth. The process by which the female transfers the fertilized eggs to the male's mouth is not clear. In any case, he fasts for as long as two months until the fry are released.

Conservation status

The IUCN Red List includes 66 siluriform species. One, the bagre graso (Rhizosomichthys totae), a pencil catfish from the Tota Lake, 9,845 ft (3,000 m) high in the Colombian Andes, is classified as Extinct. In addition, 8 species are listed as Critically Endangered; 7 as Endangered; 22 as Vulnerable; 4 as Lower Risk/Near Threatened; and 24 as Data Deficient.

Significance to humans

Catfishes are considered one of the more important orders of vertebrates, not only because more than one-tenth of living fishes are siluriforms, but because their relationship with humans covers many aspects of life and culture. Several hundred species are now used as food, and other species will be looked upon as a source of protein in the future. Some species are greatly appreciated as game and commercial fishes and reach high market prices, but some are simply the difference between starvation and survival for millions of humans. In addition, most catfishes can be used as aquarium fishes, a business that is not only worth millions of dollars, but gives urban populations the opportunity to get in touch with a significant part of nature.

Species accounts

Resources

Barthem, Ronaldo, and Michael Goulding. The Catfish Connection. New York: Columbia University Press, 1997.

Berra, Tim M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

Burgess, Warren E. An Atlas of Freshwater and Marine Catfishes. Neptune City, NJ: T.F.H, 1989.

Ferraris, Carl J., Jr. "Catfishes and Knifefishes." In Encyclopedia of Fishes, edited by John R. Paxton and William N. Eschmeyer. San Diego: Academic Press, 1995.

Galvis, Germán, José Iván Mojica, and Mauricio Camargo. Peces del Catatumbo. Bogotá: Asociación Cravo Norte, 1997.

Helfman, Gene S., Bruce B. Collette, and Douglas E. Facey. The Diversity of Fishes. Malden, MS: Blackwell Science, 1997.

Mejía, Luz Stella, and Arturo Acero P., eds. Libro Rojo de Peces Marinos de Colombia. Bogotá: Invemar, Instituto de Ciencias Naturales, Ministerio del Medio Ambiente, 2002.

Mojica, José Iván, Claudia Castellanos, José Saulo Usma, and Ricardo Álvarez, eds. Libro Rojo de Peces Dulceacuícolas de Colombia. Bogotá: Instituto de Ciencias Naturales, Ministerio del Medio Ambiente, 2002.

Nelson, Joseph S. Fishes of the World. New York: John Wiley & Sons, 1994.

De Pinna, Mario C. C. "Phylogenetic Relationships of Neotropical Siluriformes (Teleostei: Ostariophysi): Historical Overview and Synthesis of Hypotheses." In Phylogeny and Classification of Neotropical Fishes, edited by L. Malabarba, R. Reis, R. Vari, Z. Lucena, and C. Lucena. Porto Alegre, Brazil: Edipucrs, 1998.

Ross, Stephen T. Inland Fishes of Mississippi. Jackson: University Press of Mississippi, 2001.

"All Catfish Species Inventory" [cited February 7, 2003]. "Fishbase" [cited February 7, 2003].

"Planet Catfish" [cited February 7, 2003].

"ScotCat" [cited February 7, 2003].

[Article by: Arturo Acero, MSc]

The catfishes, a highly distinctive order (also called Nematognathi) of actinopterygian fishes. In the Siluriformes the Weberian apparatus is more complex than in the related Cypriniformes. The body is usually naked or the scales are enlarged and modified into large, overlapping bony plates. There are one to four pairs of barbels, and both the pectoral and dorsal fins usually have a strong spine (see illustration). This is a large group, including about 26 families and perhaps 2000 species, of which nearly 1200 live in South America. Catfishes are known from Eocene times. See also Actinopterygii; Cypriniformes.

Gafftopsail catfish (Bagre marinus). (After G. B. Goode, Fishery Industries of the United States, 1884)