Wels catfish (Silurus glanis, Linnaeus, 1758)
Origin: Eastern Europe and Western Asia
Size: 1 to 1,5 metres and 15 to 20 kg (up to 3 metres and 150 kg)
The Wels Catfish or Sheatfish is the 3rd biggest freshwater fish in the world! The main characteristic is the presence of 2 long barbels on the upper jaw and 4 short barbels on the lower jaw; the body is elongated; it has a long anal fin extending to the caudal fin. The colour can vary a lot, normally it is dark on the back and lighter underneath, the skin is very slimy. Like eels they can swim backwards. Feeds at night on the bottom of rivers, annelid worms, crustaceans, insects, molluscs, and fish, but also can eat frogs, rats, and birds, it is a top predator feeding on everything it can catch. Inhabits rivers, dams, and lakes with deep waters, sometimes also occurs in brackish water. The females lay the eggs in shallow waters, around 30,000 per kg of body weight, and the males guard the eggs until they hatch.
The native range of the Wels Catfish extends from Germany to eastern Europe, including Poland and southern Sweden, northern Iran and southern Turkey to the Baltic States and Russia and to the Aral Sea. This species is now established in several countries to the west and south of its native range: Bosnia-Herzegovina, Spain, Portugal, Denmark, Tunisia, Italy, Syria, Croatia, Turkey, UK, France, The Netherlands, and China. The routes of introduction are mainly recreational angling, aquaculture, and biological control agent. Due to its size and quality, it is a very famous edible fish all over Europe.
The Wels Catfish was introduced illegally in Spain in 1974 in the Ebro River; in 1998 some fisherman introduced illegally in Tagus River in Spain; in 2006 the species was observed for the first time in Portugal but only in 2014 its presence was confirmed. Nowadays it is present along Tagus River and dams along the river and already have been seen in Douro River. In the last years, the population has been increasing. This species is a top predator and negatively affects the biodiversity of the rivers as well as the economic activities.
Portugal and Spain have a project together named Life Invasaqua which aims to stop the invasive species in rivers and lakes in both countries.