Wels catfish

 

Wels catfish
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Siluriformes
Family:	Siluridae
Genus:	Silurus
Species:	S. glanis
Binomial name
Silurus glanis Linnaeus, 1758

The wels catfish ( /ˈwɛls/ or /ˈvɛls/;^[1] Silurus glanis), also called sheatfish, is a large catfish found in wide areas of central, southern, and eastern Europe, and near the Baltic and Caspian Seas. 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, insects, crustaceans, and fish including other wels catfishes; the larger ones also eat frogs, mice, rats and aquatic birds such as ducks. It is found from the United Kingdom all the way east to Kazakhstan and south to Slovenia.

 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 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 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.^{[citation needed]}

 Size

Silurus glanis. Syr Darya River in Kazakhstan, Baikonur area.

With a possible total length up to 3 m (9.8 ft) and a maximum weight of over 150 kg (330 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 200–250 kg (440–550 lb) heavy, 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).^[2] In 1856, K. T. Kessler^[3] wrote about specimens from Dniepr which were over 5 m (16 ft) long and weighed up to 400 kg (880 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 lb), whereas a hypothetical specimen of 5 m (16 ft) would theoretically weigh about 700 kg (1,500 lb) or more.
Most wels catfish are only 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 normally extremely rare. At 1.5 m (4 ft 11 in) they can weigh 15–20 kilograms (33–44 lb) and at 2.2 m (7 ft 3 in) they can weigh 65 kilograms (140 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 kilograms (200 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 (320 lb) for a 2.78 m (9 ft 1 in) long specimen from the Po Delta in Italy.^[4] Other reports of larger wels (around 5 m (16 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 Austrian 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 lb), according to the fisherman.^[5]

 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 Victoria 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.

 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.