Helminth Parasites of Invasive Freshwater Fish in Lithuania.

Simple Summary: In this paper, we studied the parasitic worms of invasive fish in Lithuania. We focused on four fish species foreign to Lithuanian freshwaters, namely the monkey goby (Neogobius fluviatilis), the round goby (Neogobius melanostomus), the stone moroko (Pseudorasbora parva), and the Chinese sleeper (Perccottus glenii). In total, we examined 278 fish from 13 freshwater bodies and found 29 species of parasitic worms. Most of them were found to be juvenile and we used morphological and DNA-based methods to identify these parasitic worms. The monkey goby was the most infected fish species, carrying 18 species of parasitic worms, while the Chinese sleeper was, surprisingly, not infected. Most of the parasitic worms we found were already present in fish in Lithuania, but seven were only found within the invasive fish species we examined. This means that these fish likely brought some parasites with them when they were first introduced to Lithuanian freshwaters and are also capable of carrying and spreading local Lithuanian parasites. This novel information is important, as it helps us to better understand how invasive fish might be affecting ecosystems beyond the well-known effects that they have on habitats and other local animals. Freshwater ecosystems in Lithuania are threatened by the introduction of invasive fish species including Neogobius fluviatilis, N. melanostomus, Perccottus glenii, and Pseudorasbora parva. Data on helminth parasites of these fishes have not been comprehensively studied, with only two reports on parasites of N. melanostomus from the Curonian Lagoon and Baltic Sea, Lithuania. We examined 278 fish individuals representing 4 invasive species from 13 waterbodies. Using morphological and molecular analyses, we identified 29 helminth taxa representing 15 digenean trematodes, 6 nematodes, 4 cestodes, 2 acanthocephalans, and 2 monogeneans. With 18 species, N. fluviatilis had the highest helminth diversity, followed by N. melanostomus (11 species) and Ps. parva (8 species). Perccottus glenii was found to be free from helminth infection. The availability of historical information on the native fish parasites in Lithuania allowed us to conclude that out of the 29 recorded species, invasive fish serve as hosts for 22 local fish helminth species, while 7 helminth species have been reported exclusively in invasive fish. Based on newly obtained and previously published data, a total of 34 helminth species parasitise invasive fish in Lithuania, of which 30 use these fish as intermediate or paratenic hosts. [ABSTRACT FROM AUTHOR]