Common names for S. glanis are wels catfish or sheatfish.
Northern pike (Esox lucius) and humans are two predators of Silurus glanis. Their large size protects adults from many predators. Smaller fish may be protected somewhat by their dorsal spines.
Known Predators:
The elongated, scaleless body has a strong upper body and a laterally flattened tail. Silurus glanis varies in color. The upper side is usually a dark color and the flanks and belly are more pale. The fins are brownish. The body has a mottled appearance that is sometimes accompanied by brown spots. These catfish can grow to be quite large, perhaps as large as 3 meters long. A maximum reported weight was 220 kg. Most individuals reach sizes between 1.3 and 1.6 meters. Silurus glanis reach an average of 45 kg and has been considered one of the largest freshwater fish in its range.
Silurus glanis individuals have 1 dorsal spine and 4 to 5 dorsal soft rays, 1 anal spine and 90 to 94 anal soft rays, and a caudal fin with 17 rays. They have paired pectoral fins with 1 spine and 14 to 17 soft rays each. Their paired pelvic fins are positioned behind the dorsal fin with 1 spine each and 11 to 12 soft rays each.
There are several members in the family Siluridae. Silurus glanis is distinguished by its smaller dorsal fin, only two pairs of barbels, and the caudal fin being distinct from the anal fin.
Sex can be determined by the flap of skin behind the vent, in males it is thin and comes to a point, females have a thicker and shorter flap of skin.
Range mass: 220 (high) kg.
Average mass: 45 kg.
Range length: 3 (high) m.
Average length: 1.3-1.6 m.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
The longest know lifespan in the wild is 80 years old for S. glanis. The expected lifespan in the wild is as high as 20 to 30 years old.
Range lifespan
Status: wild: 80 (high) years.
Typical lifespan
Status: wild: 20 to 30 years.
Average lifespan
Status: wild: 20 to 30 years.
Average lifespan
Status: captivity: 60 years.
Silurus glanis is found primarily in large rivers and lakes and in deep water near dams. These catfish sometimes enter brackish water in the Black Sea and Baltic Sea.
Range depth: 0 to 30 m.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; brackish water
Silurus glanis, sheatfish or wels catfish, is native to eastern Europe and Asia. It has been introduced to several other areas including Germany, France, Spain, England, Greece, Turkey and the Netherlands.
Biogeographic Regions: palearctic (Introduced , Native )
Silurus glanis fry feed on plankton during their first year of life. When they reach larger sizes they begin to eat worms, snails, crustaceans, aquatic insects, and small fish. At adult sizes they will also prey on ducks, voles, crayfish, fish, eels, frogs, rats, coypu, and snakes. They use the incredible suction created by suddenly opening their large mouths to take in prey.
Both the top and bottom jaws each have hundreds of inward sloping, soft teeth used to grip prey. There are two "crushing plates" in front of the throat cavity used to crush prey before swallowing. Silurus glanis manipulate their prey prior to consumption by using several short spikes along the edge of the gill rakers.
Animal Foods: birds; mammals; amphibians; reptiles; fish; carrion ; insects; mollusks; terrestrial worms; aquatic crustaceans; zooplankton
Plant Foods: phytoplankton
Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore ); planktivore
Silurus glanis is a commercial fish consumed by humans. This fish has boneless white flesh that is low in fat and highly palatable. Technological research for artificial reproduction, population genetics and conservation problems have been developed over the past 10 years in the Czech Republic, France and other European countries. It is also a valued game fish in European countries.
Positive Impacts: food
Silurus glanis introductions have been implicated in declining populations of other commercial fishes.
The larvae hatch in approximately 3 days, measuring around 7 mm, and begin feeding on plankton. These fish grow quickly and can reach between 1.5 and 4.5 kg in their first year.
Silurus glanis populations appear to be stable. They are protected by Appendix III of the Bern Convention. In areas where these fish have been introduced, negative ecological consequences have been noted.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
Silurus glanis individuals use their barbels and olfactory buds to sense chemical cues in the water. They are thought to be extraordinarily sensitive to chemical stimuli. They also have a lateral line system that helps them detect water movement. Silurus glanis individuals may use path analysis to track prey. One study found that S. glanis can track the three-dimensional swim path of a guppy and successfully attack it without the presence of light. Little is known about communication in these mainly solitary animals.
Perception Channels: tactile ; chemical
Silurus glanis carry bacterial diseases that can be transmitted to other fish. They are important predators of fish, crustaceans, small mammals, and aquatic birds.
Commensal/Parasitic Species:
There is little known about mating behavior in this species. Males create nests where females deposit their eggs. Males then guard the eggs until they hatch.
Mating System: polygynandrous (promiscuous)
The male creates a shallow depression that will hold thousands of eggs laid by the female. The eggs are protected by the male until they hatch. Females can lay about 30,000 eggs per kilogram of body weight. Males grow faster and mature earlier than females. One study found that males matured at 78.82 cm at age 3 and females matured at 87.05 cm at age 4.
Breeding interval: Wels catfish breed annually during the spring.
Breeding season: Breeding/spawning season runs from May through July.
Range gestation period: 3 to 10 days.
Range time to independence: 3 to 10 days.
Average age at sexual or reproductive maturity (female): 4 years.
Average age at sexual or reproductive maturity (male): 3 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Average age at sexual or reproductive maturity (male)
Sex: male: 912 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 1277 days.
The male protects the eggs until they hatch.
Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Male)
The wels catfish (/ˈwɛls/ or /ˈvɛls/; Silurus glanis), also called sheatfish or just wels,[2] is a large species of catfish native to wide areas of central, southern, and eastern Europe, in the basins of the Baltic, Black and Caspian Seas. It has been introduced to Western Europe as a prized sport fish and is now found from the United Kingdom east to Kazakhstan and China and south to Greece and Turkey.
The English common name comes from Wels, the common name of the species in German language.[2] 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').
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 chemoreceptors), 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 pectoral fins, 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 eels.
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.
The wels catfish is a long-lived species, with a specimen of 70 years old having been captured during a recent study in Sweden.[3]
With a total length possibly exceeding 3 m (9.8 ft) and a maximum weight of over 200 kg (440 lb),[4] the wels is the largest freshwater fish in Europe and Western Asia (only exceeded by the anadromous beluga sturgeon). Such lengths are rare and unproven during the last century, but there is a somewhat credible report from the 19th century of a wels catfish of this size. Brehms Tierleben cites Heckl's and Kner's old reports from the Danube about specimens 3 m (9.8 ft) long and 200–250 kg (440–550 lb) in weight, and Vogt's 1894 report of a specimen caught in Lake Biel which was 2.2 m (7 ft 3 in) long and weighed 68 kg (150 lb).[5] In 1856, K. T. Kessler wrote about specimens from the Dnieper River which were over 5 m (16 ft) long and weighed up to 400 kg (880 lb).[6] (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.)[7]
Most adult wels catfish are about 1.3–1.6 m (4 ft 3 in – 5 ft 3 in) long; fish longer than 2 m (6 ft 7 in) are a rarity. At 1.5 m (4 ft 11 in) they can weigh 15–20 kg (33–44 lb) and at 2.2 m (7 ft 3 in) they can weigh 65 kg (143 lb).
Only under exceptionally good living circumstances can the wels catfish reach lengths of more than 2 m (6 ft 7 in), as with the record wels catfish of Kiebingen (near Rottenburg, Germany), which was 2.49 m (8 ft 2 in) long and weighed 89 kg (196 lb). Even larger specimens have been caught in Poland (2,61 m. 109 kg.), the former Soviet states (the Dnieper River in Ukraine, the Volga River in Russia and the Ili River in Kazakhstan), France, Spain (in the Ebro), Italy (in the Po and Arno), Serbia (in Gruža Lake, where a 2.4 m (7 ft 10 in) long specimen weighing 117 kg (258 lb) was caught on 21 June 2018[8][9] and the Danube river, where a catfish measuring 275 cm and weighing 117 kg was caught at Đerdap gorge in the same year[10]), 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,[11] weighed 134.97 kg (297.6 lb), although there are recent anecdotal reports of larger wels exceeding 140 kg (300 lb).[12][13][14]
Exceptionally large specimens are rumored to attack humans in rare instances, a claim 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 66 kg (145 lb) and one of 74 kg (164 lb), of which two attempted to attack him following their release. A report in the Austrian 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 barely escaped from the fish, which he estimated to have weighed over 100 kg (220 lb).[15]
Like most freshwater bottom feeders, the wels catfish lives on annelid worms, gastropods, insects, crustaceans and fish. Larger specimens have also been observed to eat frogs, snakes, rats, voles, coypu and aquatic birds such as ducks,[16] even cannibalising on other catfish. A study published by researchers at the University of Toulouse, France, in 2012[17] documented individuals of this species in an introduced environment lunging out of the water to feed on pigeons on land.[18] Out of the beaching behaviour observed and filmed in this study, 28% were successful in bird capture. Stable isotope analyses of catfish stomach contents using carbon 13 and nitrogen 15 revealed a highly variable dietary composition of terrestrial birds. This is likely the result of adapting their behaviour to forage on novel prey in response to new environments upon its introduction to the river Tarn in 1983[19] since this type of behaviour has not been reported within the native range of this species. They can also eat red worms in the fall, but only the river species.
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.[20]
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.[21]
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.[22] They were imported from Hungary in 1988 and were washed into the Itajaí-Açu river after a flood caused their tanks to overflow. In 2006, a specimen weighing 86 kg (189.5 lbs) and 1.85 m (6 ft) long was captured in Blumenau, suggesting the catfish have survived and possibly be reproducing.
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.[23] In Sweden it persists only in a few lakes and rivers, and is now considered as near threatened.[24] Recent genetic studies have furthermore found that the Swedish populations harbors low genetic diversity and are genetically isolated and differentiated from each other,[23][25] highlighting the need for conservation attention.
Only the flesh of young wels catfish specimens is valued as food. It is 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.
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.[26]
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 "double[d] round" and attempted to bite his calf.[27]
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:
The wels catfish (/ˈwɛls/ or /ˈvɛls/; Silurus glanis), also called sheatfish or just wels, is a large species of catfish native to wide areas of central, southern, and eastern Europe, in the basins of the Baltic, Black and Caspian Seas. It has been introduced to Western Europe as a prized sport fish and is now found from the United Kingdom east to Kazakhstan and China and south to Greece and Turkey.
