Detection of a neglected introduction event of the invasive fish Perccottus glenii using parasitological analysis

The fish Perccottus glenii was introduced into Europe one hundred years ago from Eastern Asia, with several initial introduction points. We used parasitological analysis to verify homogeneity-of-origin of P. glenii populations in the middle part of a large river basin where this invasive fish was documented as having an aquarium-release origin. Among others, we detected populations of P. glenii with the host-specific cestode Nippotaenia mogurndae. This supports a non-aquarium introduction of the host due to the complex life cycle of the cestode, requiring an intermediate host that is unlikely in a captive environment. Nippotaenia-negative populations were recorded in the upper and middle Moscow River basin (supporting aquarium release), but Nippotaenia-positive populations were in its lower section, as well as in the Klyazma and Tsna River basins (indicating non-aquarium release). These three rivers are tributaries of the Oka. Thus, populations within the Oka River basin are derived from at least two separate introduction events from different sources. This investigation extends our knowledge regarding the number and geographic locations of initial introduction points for this rapidly spreading invasive species. It also highlights the importance of a comparative approach as a means to address seemingly intractable issues in invasion ecology.