The European catfish (Silurus glanis), Europe’s largest freshwater fish, is rapidly establishing itself as an invasive species in Portugal. First reported in the region in 2014, this apex predator can grow up to 2.8 meters long and weigh up to 130 kilograms. Its lack of natural predators, high fecundity, and extended breeding season significantly enhance its invasive potential.
Prolonged Breeding Season Increases Reproductive Success
A recent study conducted by researchers from MARE-ULisboa and published in the Journal of Vertebrate Biology reveals that European catfish have an unusually long breeding season—lasting nearly five months, from February to June. This extended spawning period gives their offspring better chances of survival by spreading out hatching times, especially during hydrological events like spring floods. It also reduces intra-species competition for food among juvenile catfish.
Lead researcher Christos Gkenas noted:
“What surprised us was not their size or fecundity, but the fact that they spawn over such a long period and produce unusually large oocytes, over 3 mm in diameter.”
High Fecundity and Early Maturity Accelerate Population Growth
European catfish are prolific breeders. A single female can produce up to 500,000 oocytes in one breeding season. The study also found that individuals reach sexual maturity at just 70 cm in length—roughly three years of age—despite having a lifespan of up to 70 years.
Over two years (January 2022 to November 2023), researchers captured nearly 700 catfish in the Lower River Tagus using electrofishing and gill nets to analyze their reproductive patterns. The gonadosomatic index (GSI) was tracked across seasons, correlating reproductive activity with water temperature, data sourced from the SNIRH database.
Urgent Need for Management and Control
According to Filipe Ribeiro, co-author of the study:
“Controlling this invasive species requires targeted removal of larger individuals, which contribute disproportionately to population growth due to their higher fecundity.”
The threat is particularly serious in protected ecosystems, such as the International Tagus Natural Park, where European catfish populations are dense. As part of the LIFE-PREDATOR project, researchers recently removed over 1,200 kg of catfish (approx. 100 individuals) in just three days from a 10 km stretch of the Ponsul River.
“Creating dedicated teams for catfish capture and removal is essential to mitigate their ecological impact in Portugal,” Ribeiro emphasized.
Citation:
Gkenas, C., Sequeira, V., Ribeiro, D., Gago, J., Dias, D., Verma, C.R., Kumkar, P., & Ribeiro, F. (2025). Reproductive traits of the European catfish, Silurus glanis, during the early stages of invasion. Journal of Vertebrate Biology. DOI: 10.25225/jvb.24122
Source: University of Lisbon