New study on Siluro reproduction provides new data for its management

A recent study conducted by MARE researchers has provided new insights into the siluro (Silurus glanis), the invasive European catfish that has spread to the Tagus River. This top predator, with no natural enemies in the region, can reach 2.8 meters and 130 kg, and stands out for its impressive reproductive capacity, with females producing up to half a million oocytes.  

First detected in Portugal in 2014, the siluro quickly became an environmental concern. The study, carried out as part of the LIFE-PREDATOR project, is the first to analyze the reproductive biology of populations of this species in the Iberian Peninsula and one of the few carried out in areas that have already been invaded.

“What we discovered is that this fish grows quickly and that its reproductive capacity is directly linked to its body size,” explains Christos Gkenas, a researcher at MARE and first author of the study. “We were surprised to realize that the reproduction period lasts almost five months and that its oocytes can exceed 3 mm in diameter, a considerable size.”

To gain a better understanding of siluro reproduction, the researchers caught nearly 700 specimens using electrofishing and gillnets. They concluded that the spawning period occurs between February and June, a strategy that allows the larvae a greater chance of survival, even in the face of spring floods, and reduces competition between the juveniles. Another relevant finding is that siluros reach sexual maturity at the age of three, at around 70 cm in length, an early development for a species that can live up to 70 years.

The researchers warn of the need for control measures to reduce the siluro population in the Tagus. “Our focus should be on removing the largest specimens, since they are the ones with the highest fecundity,” explains Filipe Ribeiro, the study's coordinating researcher. “The density of this species is worrying, especially in protected areas such as the International Tagus Natural Park. Last fall alone, as part of the LIFE-PREDATOR project, we managed to remove around 1,200 kg of silurs in just three days, along a 10 km stretch of the Ponsul River.”

The creation of specialized teams to capture and eliminate these fish is essential to mitigate their impact,” he concludes.