Researchers from MARE ULisboa discover that the European catfish, an invasive species in Portugal, has a prolonged breeding season, enhancing its invasive potential

The European Catfish is the largest freshwater fish in Europe, reaching up to 2.8 meters in length and 130 kg in weight. It was first detected in Portugal in 2014. As a top predator, it has no natural enemies and exhibits high fecundity, with females capable of producing up to half a million oocytes (unfertilized eggs). “This is not new information, as this invasive species reaches large sizes, and there is a direct relationship between abdominal cavity volume and the total number of oocytes produced,” said Christos Gkenas, a researcher at MARE-ULisboa and the study’s lead author. “What surprised us was that this fish has a prolonged breeding season, lasting almost five months, and that its oocytes are quite large, reaching over 3 mm in diameter.”

Over two years, from January 2022 to November 2023, nearly 700 catfish were captured using electrofishing and gill nets. The researchers found that the species spawns between February and June. This strategy allows its offspring to have different survival opportunities when facing extreme hydrological events (e.g., spring floods) and helps avoid competition for food resources among juveniles. The study also determined that European Catfish individuals reach sexual maturity at around 70 cm in length (approximately three years of age), which is considered early given that the species can live up to 70 years.

“Our work is crucial for controlling this species' population because our efforts should focus on removing larger individuals, which have higher fecundity,” said Filipe Ribeiro, the study's lead researcher, also from MARE-ULisboa. “The density of these animals is particularly high in protected areas, such as the International Tagus Natural Park. In October, as part of the LIFE-PREDATOR project, we removed approximately 1,200 kg of Catfish—about 100 individuals—in just three days from a small 10 km stretch of the Ponsul River.”

“The establishment of capture and removal teams to reduce Catfish populations is essential to mitigate the impact of this massive invader in Portugal,” Ribeiro concluded.

The LIFE-PREDATOR project titled “LIFE Predator – Preventing, Detecting, and Reducing the Spread of Silurus glanis in Southern European Aquatic Systems to Protect Aquatic Biodiversity”  is funded by the European Union’s LIFE Program, is coordinated by the National Research Center in Italy and involves 11 researchers from three countries and will continue until August 2027.