The English common name comes from , the common name of the species in German language.
[ Wels is a variation of Old High German wal, from Proto-Germanic *hwalaz – the same source as for whale – from Proto-Indo-European *(s)kʷálos ('sheatfish').
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Evolution
The earliest known fossil remains of the wels catfish are from the late Miocene (about 5.3 million years ago) of Ukraine. Potentially slightly older but less well-preserved remains from 6-7 million years ago are also known from the same region. During this time period, the dominant catfish in eastern Europe appears to have been the modern Soldatov's catfish ( S. soldatovi), now only found in eastern Asia, which was better adapted to the warmer climate. The wels catfish may have been restricted to a single refugium in the Ponto-Caspian region around this point. During the Pliocene, the wels catfish appears to have expanded its range and gradually supplanted Soldatov's catfish, up to the latter's Local extinction from the region during the Piacenzian. It is thought that the more adaptable wels catfish was more tolerant to the cooling and drying trend over this period, and the increased seasonality caused by it.
Description
The wels catfish's mouth contains lines of numerous small teeth, two long barbels on the upper jaw and four shorter barbels on the lower jaw. It has a long anal fin that extends to the caudal fin, and a small sharp dorsal fin relatively far forward. The wels relies largely on hearing and smell for hunting prey (owing to its sensitive Weberian apparatus and ), although like many other catfish, the species exhibits a tapetum lucidum, providing its eyes with a degree of sensitivity at night, when the species is most active. With its sharp , it creates an eddy to disorient its victim, which the predator sucks into its mouth and swallows whole. The skin is very slimy. Skin colour varies with environment. Clear water will give the fish a black color, while muddy water will often tend to produce green-brown specimens. The underside is always pale yellow to white in colour. Albinistic specimens are known to exist and are caught occasionally. With an elongated body-shape, wels are able to swim backwards like .
The female produces up to 30,000 eggs per kilogram of body weight. The male guards the nest until the brood hatches, which, depending on water temperature, can take from three to ten days. If the water level decreases too much or too fast the male has been observed to splash the eggs with its tail in order to keep them wet.
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Size
The wels is one of the largest freshwater fish in Europe and Western Asia, only exceeded by the fish migration Atlantic and beluga sturgeon. Most adult wels catfish are about long; fish longer than are a rarity. At they can weigh and at they can weigh .
Only under exceptionally good living circumstances can the wels catfish reach lengths of more than about . Examples include the record wels catfish of Kiebingen (near Rottenburg, Germany), which was long and weighed . Even larger specimens have been caught in Poland (2,61 m 109 kg), the Czech Republic (2,64 m [Archived at Ghostarchive and the
target="_blank" rel="nofollow"> Wayback Machine: ]), and Greece, where this fish was introduced a few decades ago. Greek wels grow well thanks to the mild climate, lack of competition, and good food supply.
The heaviest authenticated specimen, captured from the river Po by a Hungarian fisherman in 2010,
The maximum total length may possibly exceed with a maximum weight of over .[Brehm, Alfred; Brehms Tierleben II - Fish, Amphibians, Reptiles 1] In 1856, K. T. Kessler wrote about specimens from the Dnieper River which were over long and weighed up to .[Mareš, Jaroslav; Legendární příšery a skutečná zvířata, Prague, 1993] (According to the Hungarian naturalist Ottó Hermann 1835-1914, catfish of 300–400 kilograms were also caught in Hungary in the old centuries from the Tisza river.)[Ottó Hermann: A Book of Hungarian Fishing (A magyar halászat könyve), p. 340, [3]]
Exceptionally large specimens are rumored to attack humans in rare instances. This claim was investigated by extreme angler Jeremy Wade in an episode of the Animal Planet television series River Monsters following his capture of three fish, two of about and one of , of which two attempted to attack him following their release. A report in the newspaper Der Standard on 5 August 2009, mentions a wels catfish dragging a fisherman near Győr, Hungary, under water by his right leg after he attempted to grab the fish in a hold. The man reported he barely escaped from the fish, which he estimated to have weighed over .[ Der Standard, 2009-08-05. Waller-Wrestling im ungarischen Fischerteich. Retrieved 2009-08-06. ]
Diet
Like most freshwater bottom feeders, the wels catfish lives on annelid worms, Gastropoda, , and fish. Larger specimens have also been observed to eat , , , , coypu and aquatic such as , even cannibalising on other catfish.
The wels catfish has also been observed taking advantage of large die-offs of Asian clams to feed on the dead clams at the surface of the water during the daytime. This opportunistic feeding highlights the adaptability of the wels catfish to new food sources, since the species is mainly a nocturnal bottom-feeder.
Distribution and ecology
The wels catfish lives in large, warm lakes and deep, slow-flowing rivers. It prefers to remain in sheltered locations such as holes in the riverbed, sunken trees, etc. It consumes its food in the open water or in the deep, where it can be recognized by its large mouth. Wels catfish are kept in fish ponds as food fish.
An unusual habitat for the species exists inside the Chernobyl exclusion zone, where a small population lives in abandoned cooling ponds and channels at a close distance to the decommissioned power plant. These catfish appear healthy, and are maintaining a position as top predators in the aquatic ecosystem of the immediate area.
As introduced species
There are concerns about the ecological impact of introducing the wels catfish to regions where it is not native. Following the introduction of wels catfish, populations of other fish species have undergone steep declines. Since its introduction in the Mequinenza Reservoir in 1974, it has spread to other parts of the Ebro basin, including its tributaries, especially the Segre River. Some endemic species of Iberian barbels, genus Barbus in the Cyprinidae that were once abundant, especially in the Ebro river, have disappeared due to competition with and predation by wels catfish. The ecology of the river has also changed, with a major growth in aquatic vegetation such as algae.
The wels catfish may have established a population in Santa Catarina, Brazil.
Conservation status
Although Silurus glanis is not considered globally endangered, the conservation status varies across the species native distribution range. In the northern periphery of the distribution, the species has been declining over the last centuries and was extinct from Denmark in the 1700s and from Finland in the 1800s.
As food
Only when younger is the wels generally valued as food. The flesh is more palatable when the fish weighs less than 15 kg (33 lb). Larger than this size, the fish is highly fatty and additionally can be loaded with toxic contaminants through bioaccumulation due to its position at the top of the food chain. Large specimens are not recommended for consumption, but are sought out as sport fish due to their combativeness. A common lure for Wels catfish is a clonk, which when dropped in the water produces a distinct sound that induces them to bite.
Attacks on people
Tabloids regularly report attacks caused by various catfish that primarily affected animals (often only the role of the catfish was presumed). In April 2009, an Austrian fisherman was allegedly attacked by a catfish in one of the fishing lakes in Pér, near Győr, Hungary. However, the man reportedly managed to break free.
The Wels was the subject of an episode in the first season of the documentary television show River Monsters. Host Jeremy Wade concluded that Wels catfish in the area were not large enough to consume adult human beings, but could easily swallow a child. Wade documented instances of Wels catfish being aggressive towards humans, including a Wels he had just caught that "doubled round" and attempted to bite his calf.[Wade, Jeremy. “Chapter 2: Wels.” River Monsters: True Stories of the Ones That Didn't Get Away, Da Capo Press, a Member of the Perseus Books Group, Boston, MA, 2012, pp. 34–49. ]
Similar stories occur in the works of older natural history writers. Alfred Brehm (1829–1884), a German naturalist, published his famous work The World of Animals in the 19th century. It was also translated into Hungarian at the beginning of the 20th century. In this, Brehm or the compiling Hungarian scientists write the following:
- "Old Gesner’s (Conrad Gessner Swiss naturalist, 1516–1565) claim that catfish doesn’t spare humans either doesn’t just belong in the realm of tales, as we know of several cases that confirm that. Thus, Heckel and Kner mention that a catfish was caught at Bratislava, in the stomach of which the remains of a child corpse were found. ... Fishermen credible to Antipa (probably Romanian zoologist Grigore Antipa, 1866–1949) told me that children bathing in the stomachs of catfish were caught in the bones of their hands and feet. - Communicates Vutskits (probably Hungarian zoologist Vutskits György, 1858–1929). - A Romanian fisherman penetrated the middle of the Danube with his boat because he wanted to take a bath. While bathing, a catfish caught his legs, which he could no longer pull out of the mouth of this big-mouthed monster, and so he got to the bottom of the water. A few days later, they came across the corpse of a dead fisherman whose legs were still in the catfish's mouth, but even the greedy robber could not release his victim's legs and drowned because of it".
In June 2025 a Wels in northern Bavaria was shot dead by police officers after it bit five people in the Brombachsee. The incident attracted media attention and sparked outrage on social media.
Related species
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Aristotle's catfish ( Silurus aristotelis) from Greece, the only other native European catfish species beside Silurus glanis.
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Amur catfish ( Silurus asotus), introduced to European rivers
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Giant Lake Biwa catfish ( Silurus biwaensis) from Japan endemic to Lake Biwa.
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Soldatov's catfish ( Silurus soldatovi) from the Amur River, Russia
See also
External links
