The catfish is one of the largest fish that we currently find in the Iberian peninsula . It can measure up to two and a half meters in length and can weigh more than one hundred kilos. The catfish is one of the most voracious invasive exotic species of our rivers but little demanding with the quality of the water, it came from Central Europe to the Iberian Peninsula in the 70’s to stay.
Today, this long-lived and prolific fish – it can live up to 25 years and lay up to 30,000 eggs in each reproductive cycle – constitutes a large-scale economic and ecological challenge in more than 16 countries outside its natural distribution area.
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, Tagus and Jucar basins ; today, it is included in the Catalog of Invasive Species of the Ministry for Ecological Transition.
Opportunistic, voracious and aggressive, the young specimens devour the plankton of the water column, but in their adult phase they consume fish, amphibians, mammals and even waterfowl.
Jeremy Wade fishes a catfish in the series ‘Monsters of the River’
He prefers slow, murky waters, with deep and soft bottoms, like the dammed areas, which support an astonishing density; in the Belver reservoir, in Portugal, there may be up to 3,000 specimens, two for each meter of river.
Filipe Ribeiro, a researcher at the University of Lisbon, participates in a project promoted by the Centro de Ciencias do Mar e do Ambiente (MARE) to study the population of catfish in the last dammed section of the Tagus River and contribute to the development of a plan for your control.
” We mark the catfish with a radio transmitter that allows us to study their movements, their concentrations or their diet to inform the authorities so that they can take measures,” he explained to Efe.
The introduction of catfish in reservoirsand rivers is associated with the release of other invasive fish that serve as food, such as bleaks 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 and in the that the Efe Agency participates.
These species also contribute to the entry of non-native pathogens of which they are carriers and cause a socioeconomic impact, since they prey on native species of interest for fishing.
Francisco Pinto is a professional fisherman in the Belver reservoir, where “years ago around 50 kilos of barbels and bogues were caught daily and today none are caught”, in part because -as well as highly valued species such as the lamprey- they are devoured by the catfish
Pinto regrets that sport fishermen return to the river this and other invasive fish so that they increase in size and are more appreciated, contrary to what the law dictates, which requires removing these specimens from the water.
His opinion collides, however, with that of the interested parties themselves, who consider that their position is “more ecological”, because the presence of exotics contributes “in many cases” to the balance of the river , in favor of the native species themselves.
The mayor of the Portuguese municipality of Mora, Luis Simao, explained that the barbel was almost extinct in the Raia river, which runs through the municipal district, among other reasons because it served as food for carp and other invaders, but “the arrival of the bleak favored him”, because this fish became part of the diet of those predators.
“We are calling the carp invasive, which has been in Portugal for hundreds of years , when what should be studied are the balances that these species make in the rivers (…) an invasive should not be removed just because it is” , has underlined. There are about 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 only exist in Portugal.
“But every two years a new exotic species arrives, with a clear effect on the native ones, either due to diseases, predation or because the genetic cross between a native fish and another non-native can give rise to non-breeding hybrids,” said Filipe Ribeiro.