Wels catfish
Encyclopedia
The wels catfish also called sheatfish, is a large catfish
found in wide areas of central, southern, and eastern Europe
, and near the Baltic
and Caspian Sea
s. It is a scaleless fresh
and brackish water
fish recognizable by its broad, flat head and wide mouth. Wels catfish can live for at least thirty years and have very good hearing
.
The wels catfish lives on annelid
worms, gastropods
, insect
s, crustacean
s, and fish
including other wels catfishes; the larger ones also eat frog
s, mice
, rat
s and aquatic bird
s such as duck
s.
s 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
positioned relatively far forward. It uses its sharp pectoral fins to capture prey. With these fins, it creates an eddy to disorient its victim, which it then simply engulfs in its enormous throat. It has very slippery green-brown skin. Its belly is pale yellow or white. Colour varies with environment. Clear water will give the fish a black coloration while muddy water will often tend to produce brownish specimens. Weight and length are not correlated linearly, and also depend on the season.
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 the muscular tail in order to keep them wet.
With a possible total length up to 3 m (9.8 ft) and a maximum weight of over 150 kg (330.7 lb) it is the second largest freshwater fish in its region after the beluga sturgeon
. However, such lengths are extremely rare and could not be proved 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 Danube
about specimens 3 m (9.8 ft) long and 200 kilogram heavy, and Vogt's 1894 report of a specimen caught in Lake Biel
which was 2.2 m (7.2 ft) long and weighed 68 kg (149.9 lb). In 1856, K. T. Kessler wrote about specimens from Dniepr which were over 5 m (16.4 ft) long and weighed up to 400 kg (881.8 lb). These reports, however, cannot be validated today for lack of physical evidence. Another point which makes these data unreliable is the abnormal length to weight ratio, a typical trait of big-fish-stories. A wels of 3 m (9.8 ft) would weigh much less, around 150 kg (330.7 lb), whereas a hypothetical specimen of 5 m (16.4 ft) would theoretically weigh about 700 kg (1,543.2 lb) or more.
Most wels catfish are only about 1.3 metre long; fish longer than 2 m (6.6 ft) are normally extremely rare. At 1.5 m (4.9 ft) they can weigh 15–20 kg (33.1–44.1 ) and at 2.2 m (7.2 ft) they can weigh 65 kilograms (143.3 lb).
Only under exceptionally good living circumstances can the wels catfish reach lengths of more than 2 m (6.6 ft), as with the record wels catfish of Kiebingen (near Rottenburg, Germany), which was 2.49 m (8.2 ft) long and weighed 89 kilograms (196.2 lb). This giant was surpassed by some even larger specimens from Poland
, Ukraine
, France
, Spain
(in the River Ebro), Italy
(in the River Po and River Arno), and Greece
, where this fish was released a few decades ago. Greek wels grow well thanks to the mild climate, lack of competition, and good food supply. The largest accurate weight was 144 kg (317.5 lb) for a 2.78 m (9.1 ft) long specimen from the Po Delta in Italy. Other reports of larger wels (around 5 m (16.4 ft) or more) are unlikely and are often regarded as typical big fish stories or in some cases misidentifications of the now rare sturgeon.
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
. A report in the Austria
n newspaper Der Standard
on August 5, 2009, mentions a wels catfish dragging a fisherman near Győr
, Hungary
, under water by his right leg after the man attempted to grab the fish in a hold. The man barely escaped with his life from the fish, which must have weighed over 100 kg (220.5 lb), according to the fisherman.
in Africa
, where Nile perch
(available in stores as Lake Victoria perch) were introduced and rapidly caused the extinction
of numerous indigenous species. This severely impacted the entire lake, destroying much of the original ecosystem
. The introduction of foreign species
is almost always a burden on the affected ecosystem. Following the introduction of Wels catfish are fishes whose number is in clear and rapid decline. Since its introduction in the reservoir Mequinenza in 1974 - has spread to other parts of the Ebro basin over Ebro
and its tributaries, especially river Segre. Some endemics species of iberian barbels, genus Barbus
in the Cyprinidae, having once been abundant especially in the Ebro river, competition and predation by wels catfish has caused its complete disappearance in the middle channel Ebro
around 1990. The ecology of the river also, has now a major development in the amount of aquatic vegetation, seaweed and algae. Barbel species from mountain stream tributary of the Ebro that wels catfish has not colonized, were not affected.
Catfish
Catfishes 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...
found in wide areas of central, southern, and eastern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, and near the Baltic
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
and Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...
s. It is a scaleless fresh
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
and brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...
fish recognizable by its broad, flat head and wide mouth. Wels catfish can live for at least thirty years and have very good hearing
Hearing (sense)
Hearing is the ability to perceive sound by detecting vibrations through an organ such as the ear. It is one of the traditional five senses...
.
The wels catfish lives on annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
worms, gastropods
Gastropoda
The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...
, insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
including other wels catfishes; the larger ones also eat frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, mice
Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
, rat
Rat
Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus...
s and aquatic bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s such as duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...
s.
Habitat
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 on the bottom, where it can be recognized by its large mouth. Wels catfish are kept in fish ponds as food fish.Physical characteristics
Wels catfish's mouth contains lines of numerous small teeth, two long barbelBarbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
s 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
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
positioned relatively far forward. It uses its sharp pectoral fins to capture prey. With these fins, it creates an eddy to disorient its victim, which it then simply engulfs in its enormous throat. It has very slippery green-brown skin. Its belly is pale yellow or white. Colour varies with environment. Clear water will give the fish a black coloration while muddy water will often tend to produce brownish specimens. Weight and length are not correlated linearly, and also depend on the season.
The female produces up to 30,000 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
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 the muscular tail in order to keep them wet.
Size
Beluga sturgeon
The beluga or European sturgeon is a species of anadromous fish in the sturgeon family of order Acipenseriformes. It is found primarily in the Caspian and Black Sea basins, and occasionally in the Adriatic Sea...
. However, such lengths are extremely rare and could not be proved during the last century, but there is a somewhat credible report from the 19th century of a wels catfish of this size. Brehms Tierleben
Brehms Tierleben
Brehms Tierleben is a reference book, first published in the 1860s,which made its author, Alfred Edmund Brehm ,known around the world.- Publishing history :...
cites Heckl's and Kner's old reports from Danube
Danube
The Danube is a river in the Central Europe and the Europe's second longest river after the Volga. It is classified as an international waterway....
about specimens 3 m (9.8 ft) long and 200 kilogram heavy, and Vogt's 1894 report of a specimen caught in Lake Biel
Lake Biel
Lake Biel or Lake Bienne is a lake in the west of Switzerland. Together with Lake Morat and Lake Neuchâtel, it is one of the three large lakes in the Jura region of Switzerland. It lies approximately at , at the language boundary between German & French speaking areas.The lake is 15 km long and up...
which was 2.2 m (7.2 ft) long and weighed 68 kg (149.9 lb). In 1856, K. T. Kessler wrote about specimens from Dniepr which were over 5 m (16.4 ft) long and weighed up to 400 kg (881.8 lb). These reports, however, cannot be validated today for lack of physical evidence. Another point which makes these data unreliable is the abnormal length to weight ratio, a typical trait of big-fish-stories. A wels of 3 m (9.8 ft) would weigh much less, around 150 kg (330.7 lb), whereas a hypothetical specimen of 5 m (16.4 ft) would theoretically weigh about 700 kg (1,543.2 lb) or more.
Most wels catfish are only about 1.3 metre long; fish longer than 2 m (6.6 ft) are normally extremely rare. At 1.5 m (4.9 ft) they can weigh 15–20 kg (33.1–44.1 ) and at 2.2 m (7.2 ft) they can weigh 65 kilograms (143.3 lb).
Only under exceptionally good living circumstances can the wels catfish reach lengths of more than 2 m (6.6 ft), as with the record wels catfish of Kiebingen (near Rottenburg, Germany), which was 2.49 m (8.2 ft) long and weighed 89 kilograms (196.2 lb). This giant was surpassed by some even larger specimens from Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
, Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
(in the River Ebro), Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
(in the River Po and River Arno), and Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
, where this fish was released a few decades ago. Greek wels grow well thanks to the mild climate, lack of competition, and good food supply. The largest accurate weight was 144 kg (317.5 lb) for a 2.78 m (9.1 ft) long specimen from the Po Delta in Italy. Other reports of larger wels (around 5 m (16.4 ft) or more) are unlikely and are often regarded as typical big fish stories or in some cases misidentifications of the now rare sturgeon.
Exceptionally large specimens are rumored to attack humans in rare instances, a claim investigated by extreme angler Jeremy Wade
Jeremy Wade
Jeremy John Wade is a British biologist, television presenter, extreme angler and writer specializing in travel and natural history. He is best known for his television series River Monsters, produced by Icon Films...
in an episode of the Animal Planet
Animal Planet
Animal Planet is an American cable tv specialty channel that launched on October 1, 1996. It is distributed by Discovery Communications. A high-definition simulcast of the channel launched on September 1, 2007.-History:...
television series River Monsters
River Monsters
River Monsters is a documentary television series that airs on Animal Planet, hosted by Jeremy Wade and produced by Icon Films of Bristol, UK. The first season aired from 5 April to 17 May 2009. A second season began airing on 25 April 2010...
. A report in the Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
n newspaper Der Standard
Der Standard
Der Standard is an Austrian national daily newspaper which is published in Vienna . It was founded by Oscar Bronner as a financial newspaper and the first edition was published on 1988-10-19...
on August 5, 2009, mentions a wels catfish dragging a fisherman near Győr
Gyor
-Climate:-Main sights:The ancient core of the city is Káptalan Hill at the confluence of three rivers: the Danube, Rába and Rábca. Püspökvár, the residence of Győr’s bishops can be easily recognised by its incomplete tower. Győr’s oldest buildings are the 13th-century dwelling tower and the...
, Hungary
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
, under water by his right leg after the man attempted to grab the fish in a hold. The man barely escaped with his life from the fish, which must have weighed over 100 kg (220.5 lb), according to the fisherman.
Ecology
There are concerns about the ecological impact of introducing the wels catfish to non-native regions. These concerns take into account the situation in Lake VictoriaLake Victoria
Lake Victoria is one of the African Great Lakes. The lake was named for Queen Victoria of the United Kingdom, by John Hanning Speke, the first European to discover this lake....
in Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, where Nile perch
Nile perch
The Nile perch is a species of freshwaterfish in family Latidae of order Perciformes. It is widespread throughout muchof the Afrotropic ecozone, being native to the Congo, Nile, Senegal, Niger, and Lake Chad, Volta, Lake Turkana and other river basins. It also occurs in the brackish waters of...
(available in stores as Lake Victoria perch) were introduced and rapidly caused the extinction
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
of numerous indigenous species. This severely impacted the entire lake, destroying much of the original ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
. The introduction of foreign species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
is almost always a burden on the affected ecosystem. Following the introduction of Wels catfish are fishes whose number is in clear and rapid decline. Since its introduction in the reservoir Mequinenza in 1974 - has spread to other parts of the Ebro basin over Ebro
Ebro
The Ebro or Ebre is one of the most important rivers in the Iberian Peninsula. It is the biggest river by discharge volume in Spain.The Ebro flows through the following cities:*Reinosa in Cantabria.*Miranda de Ebro in Castile and León....
and its tributaries, especially river Segre. Some endemics species of iberian barbels, genus Barbus
Barbus
Barbus is a ray-finned fish genus in the family Cyprinidae. The type species of Barbus is the Common Barbel, first described as Cyprinus barbus and now named Barbus barbus...
in the Cyprinidae, having once been abundant especially in the Ebro river, competition and predation by wels catfish has caused its complete disappearance in the middle channel Ebro
Ebro
The Ebro or Ebre is one of the most important rivers in the Iberian Peninsula. It is the biggest river by discharge volume in Spain.The Ebro flows through the following cities:*Reinosa in Cantabria.*Miranda de Ebro in Castile and León....
around 1990. The ecology of the river also, has now a major development in the amount of aquatic vegetation, seaweed and algae. Barbel species from mountain stream tributary of the Ebro that wels catfish has not colonized, were not affected.
As a food fish
Only the flesh of young Silurus glanis specimens is valued as food. It is palatable when the catfish weighs less than 15 kg (33 lb). Larger than this size, the fish is highly fatty and not recommended for consumption. The eggs are poisonous and should not be consumed.Related species
- Aristotle's catfishAristotle's catfishAristotle's catfish is a species of fish in the Siluridae family. It is endemic to Greece. Its natural habitat is freshwater lakes. It is threatened by habitat loss.-Source:...
(Silurus aristotelis) from Greece, the only other native European catfish species beside Silurus glanis. - Amur catfish (Silurus asotus), introduced to European rivers
- Brown bullheadBrown bullheadThe brown bullhead, Ameiurus nebulosus, is a fish of the Ictaluridae family that is widely distributed in North America. It is a species of bullhead catfish and is similar to the black bullhead and yellow bullhead...
(Ameiurus nebulosus) - Mekong giant catfishMekong giant catfishThe Mekong giant catfish, Pangasianodon gigas, is a species of catfish in the shark catfish family , native to the Mekong basin in Southeast Asia.-Species characteristics:...
on the lower reaches of the Mekong
External links
- This article includes information translated out of the German and French Wikipedias.