Trophic ecology of the invasive pond loach Misgurnus anguillicaudatus (Cantor, 1842) in NW Italy

Abstract

Biological invasions are a major factor driving biodiversity loss in freshwater ecosystems. Among invasive fish, the pond loach Misgurnus anguillicaudatus , native to temperate East Asia, has rapidly expanded across Europe and was recently listed as an Invasive Alien Species of Union Concern (European Commission, 2025). In Italy, the species has established abundant populations in rice fields and irrigation networks of the Po River basin, potentially threatening native communities. Despite its rapid spread, its trophic ecology in invaded Mediterranean systems remains poorly understood. This study characterizes the trophic ecology of M. anguillicaudatus within a network of spring-fed agricultural channels in NW Italy, an area supporting endemic and threatened native species. A total of 1,000 specimens were collected across five sampling campaigns (June 2024 - February 2025) using standardized electrofishing. Benthic macroinvertebrates were simultaneously sampled to characterise prey availability. Gut contents were analysed under stereomicroscope, identifying and counting prey to family or genus level, while detrital components were scored semi-quantitatively. Diet variation was explored using multivariate analyses (nMDS, PERMANOVA), while seasonal patterns in prey abundance and richness were tested using generalized linear models. Feeding selectivity was assessed using Ivlev’s index and the WitOMI framework to compare realised and potential seasonal trophic niches. Over 17,000 prey items were identified from 993 gut contents, with more than 98.5% belonging to aquatic taxa. Prey abundance was 72% higher in summer, whereas richness remained relatively stable across seasons. Diet composition differed significantly between seasons (R² = 0.03, p = 0.001) and marginally between size classes (R² = 0.006, p = 0.003), but not between sexes. Detrital components, particularly sediment-associated material, increased significantly during winter, indicating a seasonal shift toward more opportunistic or resource-limited feeding conditions. Feeding selectivity analysis revealed a seasonal strong preference for benthic, relatively low-mobility prey, particularly molluscs (e.g., Valvata , Physa , Lymnaea ), isopods, and dipteran larvae (e.g., Chironomidae, Simuliidae). In contrast, larger and more mobile taxa such as Ephemeroptera, Trichoptera, and Odonata were consistently avoided, suggesting that feeding was influenced by both prey preference and mouth-gape constraints. WitOMI analysis confirmed a marked and statistically significant seasonal shift in the realised trophic niche (Monte Carlo permutation test: p = 0.001), with a broader niche in summer indicating higher dietary diversification. Overall, M. anguillicaudatus emerges as a selective benthic forager, with consistent preference for soft-bodied molluscs and dipteran larvae, and with marked seasonal plasticity in resource use. These findings establish an important baseline of functional traits for M. anguillicaudatus in a previously understudied invaded system, with implications for future comparisons across environmental contexts and for management strategies under the EU Invasive Alien Species Regulation.