Features of the parasitic system formation in herbivorous fish in the aquaculture of the North-Eastern and Eastern regions of Ukraine

Abstract

The research aimed to determine the peculiarities of the formation of the parasitic system in herbivorous fish in the aquaculture of the North-Eastern and Eastern regions of Ukraine. In fish farms of the North-Eastern and Eastern regions of Ukraine, 26 species of parasites were found in herbivorous fish: 19 species in the silver carp (11 — protozoa, 1 — monogeneans, 4 — trematodes, 3 — parasitic crustaceans); 18 species in the grass carp (6 — protozoa, 1 — monogeneans, 4 — trematodes, 4 — cestodes, 3 — parasitic crustaceans); and 20 species in the bighead carp (10 — protozoa, 1 — monogeneans, 4 — trematodes, 2 — cestodes, 3 — parasitic crustaceans). 11 species (42.3%) of registered parasites were invasive; 18 species (69.2%) of the detected herbivorous fish’s parasites develop directly and 8 (30.8%) — with the participation of definitive and intermediate hosts; the fish is an additional (second intermediate) host in the life cycle of 6 species (23.1%) of parasites. Outbreaks of diseases caused by parasitic protozoa from the genera Myxobolus, Cryptobia, Chilodonella, and Ichthyophthirius have been reported in both fingerlings and two-year-olds. The protozoa from the genera Ichthyobodo, Trichodina, and Trichodinella were registered en masse only in fingerlings. Pathogens from the genus Dactylogyrus were more often registered among three-year-old silver and bighead carps. Metacercariae of Ichthyocotylurus variegatus were found en masse in fingerlings of the grass carp. Posthodiplostomum cuticola larvae in unfavorable farms were found with a high level of prevalence in fish of different age groups. Thong plerocercoids were more commonly recorded in two-year-old silver and bighead carps and fingerlings of the grass carp. The highest level of cestode infection with Bothriocephalus acheilognathi was recorded in fingerlings of the grass carp. Parasitic crustaceans Sinergasilus lieni with a high level of prevalence were registered in two-year-old and three-year-old fish. Crustaceans Lernaea cyprinacea massively affected two-year-old and three-year-old fish. Pathogens from the genera Trichodina, Cryptobia, and Chilodonella, and Dactylogyrus hypophthalmichthys, Posthodiplostomum cuticola, and Sinergasilus lieni were of the greatest epizootic significance for the silver carp; for the bighead carp — from the genus Myxobolus, (especially M. pavlovskii), Chilodonella piscicola, Ichthyophthirius multifiliis, Dactylogyrus aristichthys, Posthodiplostomum cuticola, Diplostomum spathaceum, Digramma interrupta, and Sinergasilus lieni; for the grass carp — Bothriocephalus acheilognathi, Ichthyocotylurus variegatus, Ligula intestinalis, Sinergasilus major, Lernaea cyprinacea, Ichthyobodo necator, and Ichthyophthirius multifiliis