The influence of age on the occurrence of internal parasites in perch (Perca fluviatilis L.) from Lake Goreckie in Wielkopolski National Park

European perch (Perca fluviatilis) is a widespread species of freshwater fish. The most frequently isolated parasites in this species are endoparasites, such as trematodes, cestodes and nematodes. The purpose of the study was to determine the presence of parasite species found in perch and the correlations between the occurrence of parasites and age in fish from the Lake Góreckie reserve, located in Wielkopolski National Park. Among 139 examined perch, parasites were found in 69,8%. The analysis showed parasite species from the genera Acanthocephalus, Cammallanus, Neoechinorhynchus, Triaenophorus, Proteocephalus and Tetracotylus. The most common parasitosis was taeniasis. The analyses showed that occurrence of parasites correlates with the age of perch. Older fish were more often infected with parasites, especially of the genus Triaenophorus.