How a 200-kilo fish is putting Spain’s rivers at risk

Catfish are known for their distinctive moustaches and can reach truly titanic sizes. They typically grow up to two metres in length and weigh more than 100 kilograms. However, there are specimens that have grown up to three metres and weigh nearly 270 kilograms.

In 1974, a German fisherman carelessly decided to introduce a wels catfish into the River Ebro of northeastern Spain with the idea of catching it later on. 

Unfortunately, he never did and almost 50 years later catfish have spread to several rivers and fresh bodies of water across the country, their population growing out of control and causing destruction and an imbalance in the local ecosystems.

The presence of the siluro as it is called in Spanish, a species native to the big rivers of Central and Eastern Europe, is both endangering local endemic species and also affecting the Spanish fresh fishing industry, even though there are those who argue that it's made the Ebro a big tourist attraction for amateur fishermen.

Wels catfish can now be found in the river basins of all of Spain's main ríos: the Guadalquivir, the Tajo, the Duero, the Guadiana and the Ebro.

One of the most surprising things about them is that they are voracious predators that eat other fish species, as well as many other animals they can get their mouths around.

This means that they eat a wide variety of prey from crabs to ducks, as well as endangered migratory species such as common shad and Atlantic salmon.

In the stretch of the River Ebro that runs through the city of Zaragoza, they have even been known to eat pigeons that come down to the water’s edge to drink or bathe.  

https://www.youtube.com/watch?v=yoRNAkZBT7U

Catfish are a growing problem in Spain. Females can produce up to 30,000 eggs per kilogram of their body weight and with a life expectancy of 30 years on average, some up to 80 years, it's easy to see how their populations have grown out of control. 

Currently, it is forbidden to fish and kill the wels catfish in the Ebro, as legislation states that they must be returned to the river after photos and measurements have been taken.

"We don't have catfish as big as this back in Germany," tourists at the Mequinenza Dam told Spanish  TV channel La Sexta. 

According to the Caspe Fishing Association, 100,000 people visit the area every year attracted by catfish fishing, leaving behind €9 million in indirect revenue. 

“When a population is in the first phase of colonisation, it is the only time to attack it as once it's established it's almost impossible to eradicate it,” Carlos Fernández Delgado, professor of Zoology at the University of Córdoba, told news agency EFE about the fact that it's still possible to prevent the catfish's proliferation in the Guadalquivir, even if it's too late for the Ebro.

READ ALSO: Fishermen's bait blamed for algae-filled mountain lakes in Spain

Catfish are far from the only invasive fish species causing destruction to the Spanish rivers, however. The black catfish, a species native to North America; the common carp, a fish from Asia and river perch have all caused problems for the native prey species.

Fish are just one of a wide range of organisms listed by the Spanish Catalogue of Invasive Exotic Species, prepared by the Ministry for the Ecological Transition and the Demographic Challenge (MITECO).  

The list of invasive species in Spain includes those that are altering Spain’s native ecosystems, such as killer algae, a marine species that has devastated underwater ecosystems by aggressively competing with native flora, raccoons, and tiger mosquitoes, which can carry various diseases.