Parasite co-invasion by northern pike (Esox lucius): molecular evidence and establishment of alien parasites in the Zrebar Lake

Biological invasions by apex predators can restructure the destination range through ecological turbulence. This study investigates the co-i,markedntroduction and establishment of parasites associated with the invasive northern pike, Esox lucius, in Zrebar Lake (Tigris River basin, Iran). A total of 100 specimens of pike were collected during 2020 and 2025, and two alien parasites were found: the monogenean Tetraonchus monenteron and the nematode Raphidascaris acus . The obtained ITS sequences showed 100% identity with R. acus sequences from Anzali (KM047505) and Turkey (KT633862). Compared with populations from the native range, the invasive pike population showed reduced parasite richness, prevalence, and infection intensity. However, these reductions alone are insufficient to explain the invasion success of E . lucius under the framework of the Enemy Release Hypothesis (ERH), and further evidence is required to evaluate this mechanism. Larval stages of R. acus were detected in the non-native cyprinid Carassius gibelio , indicating successful completion of the parasite life cycle in the invaded ecosystem. The present study provides evidence for parasite co-invasion and establishment associated with northern pike in Zrebar Lake. It highlights the ecological importance of invasive host–parasite interactions in freshwater ecosystems.