Infection status of helminth fauna in native and non-native freshwater fish in Jukdang stream, Korea.

Non-native species are known to pose threat to the ecological stability of indigenous communities following the introduction of pathogens into the new range thereby potentially altering the function of the ecosystem. Understanding the parasite diversity and pattern of assemblage in their introduced habitat is critical in addressing host-parasite interactions especially in environments exposed to human-mediated pressures such as heat polluted wastewater. However, despite marked environmental changes in the Korean aquatic system, parasite fauna and community structure in co-occurring native and non-native freshwater fish have gained less attention. Our study investigates for the first time the helminth infections in native and non-native freshwater fish inhabiting a thermally stable stream in the Republic of Korea. The findings showed that all non-native host species including Poecilia reticulata were parasite-free throughout the sampling period, suggesting a potential enemy release from the fish host during its introduction which may limit parasite establishment and thus contribute to their invasive success. In contrast, all helminth infections were restricted to native fish species with 22 (32.4%) of fish hosts infected in total. Misgurnus spp. and Rhodeus ocellatus exhibited more diverse helminth fauna and highest infection intensities, respectively. The most frequently encountered were trematode larval stages of Opisthorchiidae gen. sp. and Cyathocotyle sp., with continued seasonal presence in Misgurnus spp., indicating its probable role in maintaining transmission cycles. This finding enhances our understanding of parasite dynamics in a disturbed freshwater system and further raises concerns on the parasite exposure and zoonotic risk in residents of this environment.