The wels catfish, the opportunistic and voracious predator that came from central Europe

Being 2.5 m long and weighting up to 130 kg, the wels catfish (Silurus glanis) is one of the most invasive exotic species in our rivers. This fish, without demanding high water quality, came from central Europe to the Iberian Peninsula in the seventies and it hasn’t left ever since. Being able to live more than 25 years and laying up to 30,000 eggs in every reproductive cycle, this fish represents a large-scale economic and ecological challenge in more than 16 countries outside its natural range.

The spread of the wels catfish

Out of all the invasive species threatening Spain’s wildlife, one of the most damaging ones is the wels catfish, a huge freshwater fish that has taken over Spain’s river ecosystems in just a few years. Experts are warning of the potential for devastation of this species and are urging to take action to stop its rapid spread.

Its anthropogenic introduction was motivated by the interest in practicing sport fishing in the rivers and reservoirs of the Iberian Peninsula. It was detected in the Ebro basin, from where it spread across those of the Duero, Tajo and Xúquer. Nowadays it’s included in the List of Invasive Species of the Ministry for the Ecological Transition.

Opportunistic, voracious and aggressive, young individuals devour plankton from the water column, but in their adult stage they eat fish, amphibians, mammals and even waterfowl, placing themselves at the top of the food web. It prefers slow, turbid, deep, soft-bottomed waters, such as those found in dammed areas, holding a surprising density; in the Belver reservoir, in Portugal, there can be up to 3,000 wels catfish individuals, two for every meter of river.

Wels catfish introduction in reservoirs and rivers is associated with the release of other invasive fish they eat, such as common bleaks or pumpkinseeds, multiplying their negative impact on ecosystems and their balance. These species also play a role in the introduction of non-indigenous pathogens, of which they’re carriers, and, as predators of indigenous species relevant to the ecosystem and fishing activities, cause a socio-economic impact.