European catfish has 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.
in the Journal of Vertebrate Biology, 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.
-
Gonadosomatic-index (GSI) of female (dark color) and male (white color) European catfish Silurus glanis specimens in relation to water temperature (dashed line) in the Lower River Tagus (LRT). The box represents the interquartile range (IQR; 25th and 75th percentiles), and the line within the box is the median. Whiskers represent the 75th percentile + 1.5 × IQR and the 25th percentile + 1.5 × IQR. Water temperature values are shown as mean and extracted from the SNIRH database ( ). Numbers in brackets denote the number of female and male individuals used in the analysis, separated by a slash. Credit: Gkenas, C., Sequeira, V., Ribeiro, D., Gago, J., Dias, D., Verma, C.R., Kumkar, P. and Ribeiro, F., -
Logistic regression curve of the proportion of mature female (upper panel) and male (lower panel) European catfish Silurus glanis specimens with total length in the Lower River Tagus (LRT). The solid line represents the model-predicted values, the dashed lines represent the corresponding 95% confidence intervals, and the red lines indicate the respective values in the Figure. Credit: Gkenas, C., Sequeira, V., Ribeiro, D., Gago, J., Dias, D., Verma, C.R., Kumkar, P. and Ribeiro, F.
"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.
More information: Christos Gkenas et al, Reproductive traits of the European catfish, Silurus glanis, during the early stages of invasion, Journal of Vertebrate Biology (2025).
Provided by University of Lisbon
