Diurnal and seasonal behaviour of adult and juvenile European catfish as determined by radio-telemetry in the River Berounka, Czech Republic

The first telemetry study analysing behaviour of the largest freshwater predator in European rivers, Silurus glanis , was performed bimonthly during the years 2002–2004. Movement of juveniles and adults occurred mostly in the same time intervals. The only statistical differences occurred for nocturnal activity in spring and autumn. In spring and winter, activity was low with the peaks during daylight, and in autumn, maximal movement was recorded during dusk. In summer, the European catfish were active across the whole 24 h even during high-flow conditions. During all other seasons, movement was inversely related to flow rate. Maximal home ranges occurred in summer, being larger for adults. Juveniles and adults were spatially segregated. With increasing flow, fish were displaced, and individuals from both groups got closer to each other. Only juveniles migrated downstream from the upstream isolated river stretch suggesting a negative impact of lateral obstructions on the fish population structure.