Seasonal variability in the isotopic niche of the invasive channel catfish Ictalurus punctatus in Japan

The global threat posed by non-native species to biodiversity and freshwater ecosystems necessitates understanding their ecological impacts. The invasive North American channel catfish Ictalurus punctatus (Rafinesque, 1818) is such a case, having been shown to not only have considerable impacts to native biodiversity, but also to expand its range. Several decades ago, I. punctatus was introduced to Lake Kasumigaura, Japan. This study investigates the seasonal dynamics of I. punctatus’ trophic niche over three consecutive years. Stable isotopes analyses of carbon (δ 13 C) and nitrogen (δ 15 N) were utilized to assess isotopic niche variation and feeding habitat. Results demonstrate ontogenetic variations in I. punctatus ' trophic position and feeding habitat, influenced by both season and year. Ictalurus punctatus exhibited a wider isotopic niche and greater interindividual dispersion during spring and summer compared to autumn and winter. While the occupied isotopic niche space remained stable across years, significant seasonal differences were observed in 2 out of 3 years. These seasonal differences underscore the high trophic plasticity of I. punctatus , facilitating its ability to exploit a diverse spectrum of resources. This research advances our understanding of this species' trophic traits and invasiveness, emphasizing the significance of considering seasonal variations in the ecological impacts of invasive fish species.