Chronic exposure to polyethylene and tire wear particles changes the associative behaviour in cyprinid fishes

The pervasive presence of anthropogenic pollutants such as polyethylene (PE) and tire wear particles (TWPs) is increasingly impacting wildlife, including behavioural traits. However, their effects on species-specific associations remain unclear. This study investigates the effects of dietary exposure to PE and TWPs on the associative and social behaviours of native crucian carp (Carassius carassius) and invasive gibel carp (Carassius gibelio) over a 60-day period. By comparing native and invasive species, we explore how these pollutants might differentially affect species with distinct adaptive strategies, potentially influencing local biodiversity and community dynamics. Fish were exposed to 0.1% PE and TWPs through their diet and assessed using zone-derived behavioural metrics: distance travelled, cumulative duration, and turning frequency, whereas the proximity of time spent outside of the zones. While PE exposure had no significant effect, TWPs significantly altered multiple associative behavioural metrics including distance travelled, cumulative duration, turning frequency, and time spent in proximity. Crucian carp exhibited greater locomotor activity and turning frequency, reflecting increased exploration. In contrast, gibel carp showed reduced movement and turning, along with elevated proximity time, suggesting spatial withdrawal. PE had comparatively weaker behavioural effects. Contrary to expectations, the invasive gibel carp did not exhibit greater behavioural resilience but instead displayed a more conservative behavioural response under TWPs exposure. These species-specific disruptions in shoaling behaviour may have long-term ecological consequences, affecting competitive interactions and community structure in polluted freshwater environments. Our findings underscore the need for further research on how emerging contaminants influence species interactions and freshwater community dynamics.