Trematodes genus Apophallus (Trematoda: Heterophyidae) in the fauna of multicellular parasites Perca fluviatilis (Perciformes, Actinopterygii) in the Volga Delta

Abstract

The living conditions of aquatic organisms in the Volga-Caspian Sea Shipping Canal are determined by a high level of complex multifactor anthropogenic load. As a link in a unified international transport system, the canal serves as an invasive corridor for the settlement of alien organisms, including parasites. The fauna of multicellular parasites Perca fluviatilis (Perciformes) in the canal area was studied. 6 taxa of parasitic organisms have been registered. The nematode Eustrongylides excisus occupies a dominant position in the fauna of macroparasites P. fluviatilis. An alien trematode, Apophallus muehlingi, was discovered associated with the invasive mollusk Lithoglyphus naticoides; the parasite has the status of a codominant species. A specific parasite widely distributed in perch fish populations in the Volga delta, Apophallus donicus, has not been registered. The high degree of invasion of perch by A. muehlingi during the three-year study period indicates the stability of the parasitic subsystem “A. muehlingi – P. fluviatilis”, previously uncharacteristic for this host species in the lower reaches of the Volga. Currently, more favorable conditions have developed for the invasion of perch A. muehlingi than A. donicus in certain areas of the Volga delta. Thus, structural changes were found in the host-parasite relationships systems of the trematodes of the genus Apophallus, which appear in the form of a partial restructuring of the species and host structure of the fauna of macroparasites P. fluviatils in the investigated area of the river. This situation is determined by factors that are largely anthropogenic in nature – changes in the living conditions of hosts and parasites, caused by a combination of fluctuations in the level of the Caspian Sea and the discharge of the Volgograd hydroelectric station, intensive shipping (large volume of cargo transportation) and high fishing pressure. The most likely significant additional factor of changes in the nature of infection of P. fluviatils by trematodes of the genus Apophallus is currently a decrease in the stocks of populations of some massive species of cyprinid fish – the second intermediate hosts of A. muehlingi, for which the parasite is defined as specific.