Body size, condition, growth rate and parasite fauna of the invasive Perccottus glenii (Actinopterygii: Odontobutidae) from small watercourse in the Vistula River basin, Poland

For the last few decades there have been reports not only of the occurrence of new invasive species of European watercourses, but also their increasing expansion. One of such species is the Amur sleeper (Perccottus glenii). The present work contains assessment of age and length distribution, condition as well as growth rate and analysis of the parasite fauna of the Amur sleeper from the waters of the Vistula River tributary in its middle course (the Habdziński Canal). During the catch performed in 2017 and 2019, the total of 177 Amur sleepers were recorded in the studied watercourse and a statistically significant sex structure disproportion was observed. Among the specimens caught in 2017 dominant were fishes with lengths of 50.1–60.1 mm whereas in 2019 the majority of the Amur sleeper specimens measured 30.1–50.0 mm. Six age groups were recorded among the caught fish with a clear prevalence of specimens aged 1+ (70.06%). The most frequently recorded parasite of P. glenii was non-quantifiable Trichodina rostrata ciliate for which the Amur sleeper from the Polish waters appeared to be a new host. Moreover, the presence of an acanthocephalan Acanthocephalus lucii, not recorded in Poland in this host before, was observed in the chyme. Also, accidental presence of larvae of the Opisthioglyphe ranae tremadote, which is a parasite typical of amphibians, was also recorded. Despite unfavourable habitat conditions and increased volumes of biogenic substances in the waters of the Habdziński Canal, the Amur sleeper found convenient conditions to reside in this small watercourse.