Influence of Triaenophorus nodulosus invasion on morphobiological parameters of European perch (Perca fluviatilis L.) in Shatsk National Nature Park reservoirs

It was conducted comprehensive ichthyological and ichthyopatological research of European perch (Perca fluviatilis L.) populations in lakes of Shatsk National Nature Park and the impact of Triaenophorus nodulosus invasion on its size, weight and reproductive ability. Morphometric analysis, absolute and relative fecundity of fish were determined by the methods generally accepted in ichthyology. Clinical examination of fish (2,225 specimens, including European perch -1650 specimens) was performed during control catches. Simultaneously, the weight, size, and age of the fish were determined. Morphometric analysis was performed on 120 specimens of perch with the length of 104.4-194.8 mm and the weight of 16.4-177.6 g. Pathoanatomic autopsy of the fish was performed in the field and laboratory conditions. Parasitological studies were performed by the method of incomplete parasitological analysis. The extent and intensity of the invasion were determined. When conducting research on the parasitofauna of native fish species in the lakes of the Shatsk National Nature Park, it was found their infestation with helminths of various systematic positions (Triaenophorus nodulosus, Khawia sinensis, Raphidascaris. acus, and Philometroides lusiana). Perch was the most infected with the helminths. The invasion caused by the plerocercoid of Cestoda T. Nodulosus was the most intensive (18.2-56.3%, depending on the reservoir). There was a significant difference in the measurements of non-infested and infested with T. nodulosus fish individuals of the same age, we also registered significant lag in growth and a decrease in body weight among the infested specimens. A steady trend towards a decrease in fecundity parameters was also observed in infested fish. Thus, in non-infested individuals of 4-year perch, the highest individual absolute fecundity (IAF) was 6.7 thousand eggs against 3.1 thousand eggs in the infested perch (Lucimer lake). The lowest IAF -3.9 thousand eggs against 2.0 thousand eggs in the infested perch specimesn was found in Chorne Velyke lake. In non-infested individuals of 5-year perch, the highest IAF index was 9.4 thousand eggs when compared to 6.8 thousand in the infested perch (Pulemetske lake). The lowest IAF was 6.3 thousand eggs (Chorne Velyke lake). The highest IAF was recorded in perch from Pulemetske lake (34.6 thousand eggs in non-infested versus 10.3 thousand eggs in infested specimens). The lowest IAF was observed in perch from Chorne Velyke lake (9.1 and 6.6 thousand eggs, respectively). There was decrease in fish size, weight and fecundity in perch infested with Tr. nodulosus, but it did not affect the reproductive fish ability.