The influence of the biotic and abiotic factors on the state of the parasitic fauna of the hydrobionts in natural waters of the Southern Ukraine

The article observes the results of the scienti c researches conducted in 2018–2019. 198 samples of the Gobiidae shes (Neogobius uviatialis Pallas, 1814, Mesogobius batrachocephalus Pallas, 1814, Neogobius melanostomum Pallas, 1814,), as well as 78 samples of other predatory shes (Perca uviatilis Linnaeus, 1758, Sander lucioperca Linnaeus, 1758, Esox lucius Linnaeus) were subjected to the ihtyopathological analysis with such an aim. The samples were caught in the waters of the Dnipro-Buh estuary near the Dniprovske village and near the Agigol Cape in the Mykolayiv Region. The average index of the invasion extensiveness among the Gobiidae shes of the Dnipro-Buh estuary in June counted 26.6%, and the highest level of the invasion intensiveness counted – 94 – 157 metacecaria – the cryptocotyle agents. Following the sh-kill in July 2018 it was possible to notice the 114.2 % – decrease of the Gobiidae shes population. The level; of the cryptocotyle invasion of these shes reached its peak in August, counting 60.3%, and the amplitude of the invasion intensiveness waved between 102 and 211 samples. In June the level of invasion of the predatory shes (perch, pike, sander) with eustrongylides counted 63.8%, and the invasion intensiveness reached the highest point among Esox lucius Linnaeus – from 1 to 8 nematoda larvae. The 47.8 % – decrease of the amount of the predatory shes caught in the waters of the DniproBuh estuary was noticed after the sh-kill. In August the eustrongylide invasion extensiveness counted 84.3%, and the index of the invasion intensiveness was 2–12 parasites. The impact of the sh-eating birds on forming the natural focuses of the cryptocotyle and eustrongylide invasions among the main commercial shes of the Dnipro-Buh estuary was determined. Hydrochemical analysis of the waters of the Dnipro-Buh estuary was held separately to determine the reason of the mass sh-kill in July 2018. The hydrochemical analysis of the waters of the DniproBuh estuary in July showed contradictions of such points as pH, oxygen, free ammonia, and total hardness to the actual normative legal documents. The inappropriate hydrochemical condition was the reason of the sh-kill in the aquatic biological recourses. The in uence of biotic and abiotic factors on the condition of the parasitic fauna in the researched shes of the natural waters of the Southern Ukraine was determined.Key words: gobiidae shes, predatory shes, abiotioc and biotic factors, cryptocotilosis, eustrongylidosis.