Catfish

Catfishes (order Siluriformes) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores (species that eat dead material on the bottom), and even to a tiny parasitic species commonly called the candiru, Vandellia cirrhosa. There are armour-plated types and also naked types, neither having scales. Despite their name, not all catfish have prominent barbels; members of the Siluriformes order are defined by features of the skull and swimbladder. Catfish are of considerable commercial importance; many of the larger species are farmed or fished for food. Many of the smaller species, particularly the genus Corydoras, are important in the aquarium hobby.

Distribution and habitat

Extant catfish species live in inland or coastal waters of every continent except Antarctica. Catfish have inhabited all continents at one time or another.

They are found in freshwater environments, though most inhabit shallow, running water. One such species is Phreatobius cisternarum, known to live underground in phreatic habitats. Numerous species from the families Ariidae and Plotosidae, and a few species from among the Aspredinidae and Bagridae, are found in salt water.

Physical characteristics

External anatomy of catfish

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Most catfish are bottom feeders. In general, they are negatively buoyant, which means that they will usually sink rather than float due to a reduced gas bladder and a heavy, bony head.

has four pairs of barbels.]] All catfish, except members of Malapteruridae (electric catfish), possess a strong, hollow, bonified leading spine-like ray on their dorsal and pectoral fins. As a defense, these spines may be locked into place so that they stick outwards, which can inflict severe wounds. This venom is produced by glandular cells in the epidermal tissue covering the spines.

Sexual dimorphism is reported in about half of all families of catfish. The modification of the anal fin into an intromittent organ (in internal fertilizers) as well as accessory structures of the reproductive apparatus (in both internal and external fertilizers) have been described in species belonging to 11 different families.

Size

, may be fatal.]]

Catfish have one of the greatest ranges in size within a single order of bony fish. However, these records pale in comparison to a giant Mekong catfish caught in northern Thailand on May 1, 2005 and reported to the press almost 2 months later that weighed . This is the largest giant Mekong catfish caught since Thai officials started keeping records in 1981. The giant Mekong catfish are not well studied since they live in developing countries and it is quite possible that they can grow even larger.

Internal anatomy

In many catfish, the humeral process is a bony process extending backward from the pectoral girdle immediately above the base of the pectoral fin. It lies beneath the skin where its outline may be determined by dissecting the skin or probing with a needle.

The retina of catfish are composed of single cones and large rods. Many catfish have a tapetum lucidum which may help enhance photon capture and increase low-light sensitivity. Double cones, though present in most teleosts are absent from catfish.

The anatomical organization of the testis in catfish is variable among the families of catfish, but the majority of them present fringed testis: Ictaluridae, Claridae, Auchenipteridae, Doradidae, Pimelodidae, and Pseudopimelodidae. Fringes of the caudal region may present tubules, in which the lumen is filled by secretion and spermatozoa.

Catfish as food

Catfish have been widely caught and farmed for food for hundreds of years in Africa, Asia, Europe, and North America. Judgments as to the quality and flavor vary, with some food critics considering catfish as being excellent food, others dismiss them as watery and lacking in flavor. In Central Europe, catfish were often viewed as a delicacy to be enjoyed on feast days and holidays. Migrants from Europe and Africa to the United States brought along this tradition, and in the Southern United States catfish is an extremely popular food. The most commonly eaten species in the United States are the channel catfish and blue catfish, both of which are common in the wild and increasingly widely farmed. Farm-raised catfish became such a staple of the diet of the United States that on June 25, 1987, President Ronald Reagan established National Catfish Day to recognize "the value of farm-raised catfish."

Catfish is eaten in a variety of ways; in Europe it is often cooked in similar ways to carp, but in the United States it is typically crumbed with cornmeal and fried. Farm-raised catfish contains low levels of omega-3 fatty acids and a much higher proportion of omega-6 fatty acids.

Vietnamese catfish cannot be legally marketed as catfish in the US, and is subsequently referred to as swai or basa

As catfish lack scales, they are judged to not be kosher and may not be eaten by observant Jews, some Christians who follow the Torah, and observant Muslims of various schools.

Aquaculture

Catfish are easy to farm in warm climates, leading to inexpensive and safe food at local grocers. About 60% of U.S. farm-raised catfish are grown within a 65-mile (100-km) radius of Belzoni, Mississippi. Ictalurids are cultivated in North America (especially in the Deep South, with Mississippi being the largest domestic catfish producer). Channel catfish (Ictalurus punctatus) supports a $450 million/yr aquaculture industry.

Catfish raised in inland tanks or channels are considered safe for the environment, since their waste and disease should be contained and not spread to the wild.

In Asia, many catfish species are important as food. Several walking catfish (Clariidae) and shark catfish (Pangasiidae) species are heavily cultured in Africa and Asia. Exports of one particular shark catfish species from Vietnam, Pangasius bocourti, has met with pressures from the U.S. catfish industry. In 2003, The United States Congress passed a law preventing the imported fish from being labeled as catfish. As a result, the Vietnamese exporters of this fish now label their products sold in the U.S. as "basa fish." Trader Joe's has labeled frozen fillets of Vietnamese Pangasius hypophthalmus as "striper."

There is a large and growing ornamental fish trade, with hundreds of species of catfish, such as Corydoras and armored suckermouth catfish (often called plecos), being a popular component of many aquaria. Other catfish commonly found in the aquarium trade are banjo catfish, talking catfish, and long-whiskered catfish.

Catfish as invasive species

is an invasive species in Florida.]] Representatives of the genus Ictalurus have been introduced into European waters in the hope of obtaining a sporting and food resource. However, the European stock of American catfishes has not achieved the dimensions of these fish in their native waters, and have only increased the ecological pressure on native European fauna. Walking catfish have also been introduced in the freshwaters of Florida, with the voracious catfish becoming a major alien pest there. Flathead catfish, Pylodictis olivaris, is also a North American pest on Atlantic slope drainages.

Dangers to humans

While the vast majority of catfish are harmless to humans, a few species are known to present some risk. Perhaps the most notorious of these is the Candiru, due to the way it is reputed to parasitize the urethra, though there is only one well-documented case of a candiru attack on a human.

Since 2007, the Goonch catfish has also gained attention following a series of fatal underwater attacks which have been alleged by biologist Jeremy Wade to have been from unusually large goonch.

The Wels catfish has also been reputed to kill humans (especially young children), and while there are no documented cases of fatalities, larger specimens are known to cause serious injuries in rare instances. In addition, other species are reputed to be dangerous to humans as well, but with less definitive evidence.

Taxonomy

The catfishes are a monophyletic group. This is supported by molecular evidence.

The taxonomy of catfishes is quickly changing. In a 2007 and 2008 paper, Horabagrus, Phreatobius, and Conorhynchos were not classified under any current catfish families. There is disagreement on the family status of certain groups; for example, Nelson (2006) lists Auchenoglanididae and Heteropneustidae as separate families, while the All Catfish Species Inventory (ACSI) includes them under other families. Also, FishBase and the Integrated Taxonomic Information System lists Parakysidae as a separate family, while this group is included under Akysidae by both Nelson (2006) and ACSI. Many sources do not list the recently revised family Anchariidae. The family Horabagridae, including Horabagrus, Pseudeutropius, and Platytropius, is also not shown by some authors but presented by others as a true group.

The rate of description of new catfishes is at an all-time high. Between 2003 and 2005, over 100 species have been named, a rate three times faster than that of the past century. In June, 2005, researchers named the newest family of catfish, Lacantuniidae, only the third new family of fish distinguished in the last 70 years (others being the coelacanth in 1938 and the megamouth shark in 1983). The new species in Lacantuniidae, Lacantunia enigmatica, was found in the Lacantun river in the Mexican state of Chiapas.

According to morphological data, Diplomystidae is usually considered to be the most primitive of catfishes and the sister group to the remaining catfishes, grouped in a clade called Siluroidei. Recent molecular evidence contrasts the prevailing hypothesis, where the suborder Loricarioidei are the sister group to all catfishes, including Diplomystidae (Diplomystoidei) and Siluroidei; though they were not able to reject the past hypothesis, the new hypothesis is not unsupported. Siluroidei was found to be monophyletic without Loricarioid families or Diplomystidae with molecular evidence; morphological evidence is unknown that supports Siluroidei without Loricarioidea.

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References

See also

Catfish clonk fishing method Clonk fishing

All catfish species inventory

Category:Aquaculture Category:Edible fish Category:Commercial fish Category:Fish of Africa Category:Fish of Asia Category:Fish of Europe Category:Fish of South America Category:Fish of North America Category:Fish of Central America Category:Soul food