Understanding the spatial ecology of invasive fish predators is essential for developing effective management strategies. We investigated the horizontal and vertical movements, habitat use, and thermal ecology of the invasive European catfish Silurus glanis in Lake Sirio, a small, deep peri-alpine lake in north-western Italy. Fifteen individuals were tagged with acoustic transmitters equipped with depth and temperature sensors and monitored for one year using an acoustic telemetry array. European catfish occupied predominantly shallow waters throughout the year, although they shifted to deeper habitats during autumn and winter. This seasonal pattern was accompanied by marked diel variation in depth use during spring, summer, and autumn, whereas diel differences largely disappeared in winter. Consistently, vertical activity peaked at dawn and dusk and reached its highest levels during summer. Fish body temperature closely tracked ambient water temperature but remained below maximum surface temperatures during summer, indicating active selection of favourable thermal conditions. Seasonal changes were also evident in horizontal behaviour, with individuals expanding their home ranges and increasing exploratory activity during spring and summer. Although core areas shifted over time, home ranges remained comparatively stable, while low overlap among individual core areas but greater overlap among home ranges suggested spatial niche partitioning, with individuals maintaining distinct refuge areas while sharing broader foraging habitats. Habitat use further reflected these seasonal dynamics, with fish concentrating in nearshore habitats during spring and progressively increasing the use of offshore areas in autumn. These findings demonstrate marked behavioural plasticity in S. glanis and provide practical guidance for its control. Removal efforts should primarily target shallow littoral habitats around dawn and dusk, particularly during spring, summer, and early autumn, when fish activity is highest. More broadly, this study highlights the value of acoustic telemetry for supporting evidence-based management of invasive freshwater fish predators.