Siluro, the opportunistic and voracious predator who came from Central Europe

Cristina Yuste/EFEverde for Lifeinvasaqua.-

Up to two and a half meters long and weighing more than one hundred kilos, the catfish, one of the most voracious invasive exotic species in our rivers but not very demanding with the quality of the water, arrived from Central Europe to the Iberian Peninsula in the 1970s to stay.

Today, this long-lived and prolific fish – which can live up to 25 years and lay up to 30,000 eggs in each reproductive cycle – is a large-scale economic and ecological challenge in more than 16 countries outside its natural range.

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The catfish’s advance

It was man who introduced it as a species of interest for recreational fishing in rivers and reservoirs, in the case of the Iberian Peninsula in the Ebro basin, from where it spread to the Duero, Tajo and Jucar rivers; today, it is included in the Catalogue of Invasive Species of the Ministry for Ecological Transition.

Opportunistic, voracious and aggressive, the young specimens devour the plankton in the water column, but in their adult phase they consume fish, amphibians, mammals and even aquatic birds.

It prefers slow, turbid waters, with deep, soft bottoms, such as the reservoir areas, which support an astonishing density; in the Belver reservoir in Portugal, there can be up to 3,000 specimens, two for every meter of river.

Monitoring of living specimens

Filipe Ribeiro, a researcher at the University of Lisbon, is participating in a project promoted by the Centro de Ciências do Mar e do Ambiente (MARE) to study the population of catfish in the last stretch of the Tagus River reservoir and contribute to the development of a plan to control it.

“We mark the catfish with a radio transmitter that allows us to study their movements, concentrations or diet to inform the authorities so that they can take action,” he explained to Efe.

The introduction of catfish in reservoirs and rivers is associated with the release of other invasive fish that serve as food, such as alburnums or percasols, which multiplies the negative impact on the ecosystem and its balance, reports from the Life Invasaqua project, coordinated by the University of Murcia with the participation of Efeverde  from Agencia EFE.

These species also contribute to the entry of non-native pathogens of which they are carriers and cause a socio-economic impact, as they prey on native species of interest to fisheries.

Sectors affected: fishermen

Francisco Pinto is a professional fisherman at the Belver reservoir, where “years ago, about 50 kilos of barbels and bogas were caught every day and today none are caught”, partly because – like such prized species as the lamprey – they are devoured by the catfish.

Pinto regrets that sport fishermen are returning these and other invasive fish to the east river to increase their size and be more appreciated, contrary to the law, which requires these specimens to be removed from the water.

However, his opinion clashes with that of the stakeholders themselves, who consider his position “more ecological” because the presence of exotic fish contributes “in many cases” to the river’s balance, in favor of the native species themselves.

The mayor of the Portuguese municipality of Mora, Luís Simâo, explained that in the Raia River, which runs through the municipality, the barbel was almost extinct, among other reasons because it served as food for carp and other invaders, but “the arrival of the alburnum favored it,” because this fish became part of the diet of those predators.

“We are calling the carp an invader, which has been in Portugal for hundreds of years, when what should be studied are the balances that these species make in the rivers (…) you don’t have to remove an invader just because it is one,” he said.

There are around 45 species of native fish in Portuguese rivers, such as barbels, bogas or lampreys, 28 of which are endemic to the Iberian Peninsula and ten of which only exist in Portugal.

“But every two years a new exotic species arrives, with a clear effect on the native ones, whether due to disease, predation or because the genetic cross between a native fish and an allochthonous one can give rise to non-reproductive hybrids,” said Filipe Ribeiro.

Video in Portuguese

Life Invasaqua is coordinated by the  Universidad de Murcia with the participation of 8 partners: EFEverde of the Agencia EFE, UICN-Med, Museo de Ciencias Naturales-Centro Superior de Investigaciones Científicas, Sociedad Ibérica de Ictiología (SIBIC), Universidad de Navarra, Universidad de Santiago de Compostela, Universidad de Évora and Associaçao Portuguesa de Educaçao Ambiental (ASPEA)

About LIFE17 GIE/ES/000515 Life Invasaqua of the EU “Invasive alien species in freshwater and estuarine systems: awareness and prevention in the Iberian Peninsula”

Co-financed by the EU within the framework of the Life initiative and coordinated by the University of Murcia, LIFE INVASAQUA aims to contribute to the reduction of the harmful impacts of INVASIVE ALIEN SPECIES (IES) on biodiversity by raising public awareness, increasing training in the sectors involved and creating tools for an efficient early warning and rapid response system (EWRR) to manage their impact on freshwater and estuary ecosystems.