The wels catfish, Silurus glanis, is a large freshwater fish. It has an elongated, scaleless body, often mottled from dark greenish-black to brown, with a pale belly. Its distinctive features include a large, flattened head with tiny eyes and six barbels around its mouth, two of which are notably long on the upper jaw. Wels catfish can grow to substantial lengths, with some individuals reaching over 2 meters (6.7 feet) and weights exceeding 65 kg (143 pounds).
Native Range
The wels catfish is native to Central, Southern, and Eastern Europe, extending into parts of Western Asia. Its natural distribution encompasses the basins of major water bodies such as the Baltic, Black, and Caspian Seas, including river systems like the Danube, Volga, Ural, Dnieper, and Don.
Fossil evidence indicates its historical presence further west, with remains found in Belgium, suggesting a broader natural distribution across the continent. Its native reach stretches from southern Sweden and Germany eastward through Poland, down to southern Turkey and northern Iran, and across the Baltic States into Russia and the Aral Sea basin in Kazakhstan and Uzbekistan.
Ideal Aquatic Environments
Wels catfish thrive in large, warm lakes and deep, slow-flowing rivers, preferring environments with ample shelter. They are often observed near the bottom, indicating a benthic lifestyle, and tolerate a range of water conditions. The species prefers soft, muddy, or silty bottoms for burrowing and nesting during reproduction.
Abundant cover is important, including submerged trees, roots, rocks, undercut banks, dense aquatic vegetation, and woody debris for refuge and concealment. Wels catfish can tolerate low levels of salinity and have been observed in brackish coastal waters, such as parts of the Black and Baltic Seas. They also tolerate turbid and degraded water conditions, including eutrophic environments.
Wels catfish prefer warmer water temperatures, with optimal activity between 25°C and 27°C. Spawning usually occurs when water temperatures reach 18-22°C. This preference for warmer conditions influences their distribution and activity patterns, as they tend to be less active in colder waters. They are primarily nocturnal predators, using the cover of night to forage for food.
Spread Beyond Native Waters
Beyond its native range, the wels catfish has established populations in many other regions, largely due to human activity. Deliberate introductions for sport fishing and aquaculture have facilitated its spread across Western Europe and into additional parts of Asia. Countries such as the United Kingdom, Spain, Italy, France, and the Netherlands now host established populations. This expansion has been ongoing for decades, with some introductions dating back to the 19th century.
The adaptability of the wels catfish to various freshwater conditions has contributed to its successful establishment in these new areas. Its ability to colonize a wide variety of habitats, including rivers, lakes, and reservoirs, has aided its dispersal. Notable examples of successful introductions include the Po River in Italy and the Ebro River in Spain, where they have become well-established.