Wels catfish

The wels catfish (/ˈwɛls/ or /ˈvɛls/; Silurus glanis), also called sheatfish, 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. It is a scaleless freshwater fish recognizable by its broad, flat head and wide mouth. Wels catfish can live for at least fifty years. 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. Like most freshwater bottom feeders, the wels catfish lives on annelid worms, gastropods, insects, crustaceans, and fish. Larger specimens have been observed to also eat frogs, mice, rats, aquatic birds such as ducks and can be cannibalistic. A study published by researchers at the University of Toulouse, France in 2012, documented individuals of this species in an introduced environment lunging out of the water to feed on pigeons on land. Out of the beaching behaviors 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 behavior to forage on novel prey in response to new environments upon its introduction to the Tarn River in 1983 since this type of behavior has not been reported within the native range of this species. 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 respectively), although like many other catfish, the species is characterised with 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. Wels swim in a fashion similar to eels, and so can swim backwards. With a possible total length up to 5 m (16 ft) and a maximum weight of over 300 kg (660 lb), the wels catfish is the largest true freshwater fish (as opposed to anadromous or catadromous) in its region (Europe and parts of Asia). However, such lengths are rare and were hard to prove 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). 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).