Dynamics of Eustrongylidosis in Fishes in the Zaporizhzhia (Dnipro) Reservoir, Ukraine

Abstract

The parasitic nematode <i>Eustrongylides excisus</i>, Jagerskiold, 1909 (Dioctophimida: Dioctophimidae) is widespread and zoonotic. 23 fish species were studied in view of infestation by this parasite. The maximal infestation with <i>E. excisus</i> larvae were recorded in seven years after the first detection of the parasite in the reservoir in 2008. Maximal infestation rate was found in the monkey goby (90%, 8.5±0.93 spec/ind) and the common perch (79%, 17.2± 1.53 spec/ind). In pike and pikeperch, the infestation rates were half as low. In other fishes (European catfish, Eurasian daces, Prussian carp, White bream), the parasite occurred sporadically with the maximum infestation extension from 3.2 to 13.6%. The dynamics of fish eustrongylidosis in the Zaporizhzhia (Dnipro) reservoir was characterized by the following stages: increase (2008-2013), maximum development (2013-2018), and decline (2018-2023) of infestation rates. The spatial distribution of <i>E. excisus</i> was characterized by high density of infested fishes in the lower section of the reservoir owing to accumulation of silt deposits and intensive development of oligochaetes in them, which are the first intermediate hosts of the parasite. We suppose, that the decline in the infestation rates decrease in the Zaporizhzhya (Dnipro) reservoir is temporary, as the reservoir provides favorable conditions for the parasite's development cycle: progressive eutrophication and siltation; presence of intermediate and paratenic hosts; favorable conditions for the cormorants nesting - the ultimate hosts of eustrongylids.