New location, food composition, and parasitic fauna of the invasive fish Pseudorasbora parva (Temminck & Schlegel, 1846) (Cyprinidae) in Poland.
Stone moroko (Pseudorasbora parva) is considered to be one of the most invasive fishes, dispersing rapidly all over Europe and also in the freshwaters of the Baltic Sea basin. A recent survey carried out in the catchment of the lower part of the Odra River (Poland) in 2015 and 2016 revealed a large new population of stone moroko, which had colonized the creek Wardynka. The sample of 518 fish caught was dominated by age groups 1+ (341 specimens) and 2+ (99 specimens); however, older fish were also present, which means that at the moment of analysis the species had been in the Wardynka for at least 5 years. The diet was composed of copepods, amphipods, ostracods, and cladocerans, with Daphnia sp. being most frequent, which also showed the highest index of relative importance and percentage by weight in the food. The parasitic fauna composition of stone moroko in the new location involves local parasites only. Trichodinella subtilis, Diplozoon paradoxum, Apatemon gracilis, and Caryophyllaeus laticeps were found for the first time ever. The lack of parasitic species that normally occur in fish of this species was probably caused by the lack of intermediate hosts, which are necessary to complete their life cycles.