Olena Kudlai

Fish blood flukes are important parasites that can cause mortalities of their hosts. Yet, blood flukes of freshwater fish are understudied worldwide. Herein, we provide new information on the family Sanguinicolidae using specimens from freshwater fishes in Lithuania. The sanguinicolids were identified using molecular (nuclear 28S rDNA and mitochondrial cox1 DNA) and morphological data. Within the type-genus Sanguinicola, we provide the first genetic characterisation of type-species Sanguinicola armatus using newly obtained specimens from the type-host Tinca tinca (Tincidae), report new host and geographic records for Sanguinicola volgensis, and describe a new species Sanguinicola bakeri n. sp. from Blicca bjoerkna (Leuciscidae). Sanguinicola bakeri n. sp. is distinguished from congeneric species by small lateral testicular lobes, elongate ovary (occupying 16–18% of the body length) and narrow oviducal seminal receptacle. Phylogenetic analysis based on the 28S rDNA sequences confirmed the distinct status of S. bakeri n. sp. within the genus Sanguinicola. We propose a new genus, Ejsmontellus n. gen., comprising of Ejsmontellus akicola n. sp. (type-species) infecting B. bjoerkna and unidentified Ejsmontellus sp. from Leuciscus leusiscus (Leuciscidae). Ejsmontellus n. gen. is diagnosed by single columns of ventrolateral tegumental spines, elongate anterior oesophageal swelling, rudimentary posterior oesophageal swelling, compact heart shaped ovary straight vas deferens and thin-walled cirrus-sac. Phylogenetically, Ejsmontellus is distant from Sanguinicola and closest to a clade comprising of cercarial isolates from pulmonate snails from Czechia, Poland and South Africa. The new findings from commonly occurring fish species show that the diversity of the Sanguinicolidae has been underestimated.

To date, only a single species of the digenean genus Macvicaria Gibson & Bray, 1982— Macvicaria obovata (Molin, 1859)—has been reported from southern African coastal waters, infecting three fish species (two sparids and one cheilodactylid). Given the general paucity of information on digeneans from marine fishes in this region, the present study aimed to explore the diversity of these parasites in the endemic sparids the Cape white seabream Diplodus capensis (Smith) and the zebra seabream Diplodus hottentotus (Smith). By integrating molecular data (based on 28S rDNA, ITS2 rDNA, cox 1 mtDNA and nad 1 mtDNA) with morphometric and morphological characterisation, three new species of Macvicaria were identified from these fish hosts in South Africa and Namibia. These are described herein as Macvicaria umbungu , Macvicaria tsitsikamma and Macvicaria peetvermaaki . This study represents the first record of species of Macvicaria from D . capensis and is the first report of a representative of this genus from Namibia. The newly generated molecular data will be valuable for future phylogenetic studies, accurate species identification, and linking different life stages of Macvicaria spp. in southern Africa. This study provides insight into the endemism of marine fish trematodes in southern Africa and explores biogeographical links between southern Africa and the Mediterranean fish trematode fauna.

Caryophyllidean tapeworms (Cestoda) are widespread parasites of suckers (Catostomidae) in North America, but their phylogenetic relationships remain poorly understood. This study presents molecular data on species of the recently established genus Pseudoglaridacris Oros, Uhrovič et Scholz, 2018. The type species, P. laruei (Lamont 1921), a very common parasite of the white sucker Catostomus commersonii (Catostomidae) in North America, is characterised both molecularly and morphologically based on recently collected, properly fixed specimens from the type host (C. commersonii) and four species of redhorse (Moxostoma spp.), including new host and geographical records from Canada and the United States. Pseudoglaridacris laruei differs from other species in the genus by its size, being the largest species (body length up to 12.7 mm), a high number of testes (62–119) and very few (0–6) postovarian vitelline follicles. Mackiewiczus etowanum from Hypentelium etowanum and Mackiewiczus rarus from Moxostoma poecilurum in Alabama are nomina nuda. The taxonomic status of P. confusa (Hunter 1929), which occurs in ictiobines, and of P. oligorchis (Haderlie 1953), which is most probably a junior synonym of P. laruei with a reduced number of testes, is also discussed, based on molecular data indicating the presence of a putative new species from ictiobines that has not yet been described.

Trematode metacercariae are the most abundant and frequently encountered helminths in freshwater fish. Yet, accurate species identification remains challenging, potentially leading to an underestimation of trematode diversity. Using data from parasitological examinations of 1,030 fish (47 species) collected from diverse freshwater habitats in Lithuania (2022–2024), we assessed the contemporary diversity of trematode metacercariae, host associations, microhabitat preferences, and changes in diversity patterns and transmission dynamics. Through integrated morphological and molecular techniques, we identified metacercariae belonging to 51 species from eight families, more than doubling previously reported diversity (25 species). While trematode family composition remained largely unchanged – the Diplostomidae and Strigeidae remained the most diverse families – notable differences were observed at the species level. Metacercariae of the Echinochasmidae and Echinostomatidae were detected for the first time, while previously reported Clinostomidae were absent. Fish of the Leuciscidae hosted the highest trematode diversity. Host specificity of metacercariae was generally low, with most species being euryxenous. At the microhabitat level, eyes harboured the highest number of species, while muscles showed the highest metacercarial density. Notably, we detected species first genetically characterised in North America ( Echinoparyphium sp. 2 and Ichthyocotylurus sp. 2) and species potentially belonging to the genus Neogogatea , previously known only from Asia and North America, highlighting potential invasion risks and suggesting that European trematode diversity remains substantially underestimated. Future efforts should obtain molecular data from correctly identified adult specimens to resolve the identity of species currently identified only to the genus or family level, thereby enabling assessment of their geographical distributions and ecological roles.

Iceland is an isolated, sub-Arctic, oceanic island of volcanic origin in the northern North Atlantic. With a limited faunal diversity and being the most northern point in the distributional range for some species, it is an intriguing model region to study parasite biodiversity and biogeography. Since 2006, there has been a history of intense biodiversity discoveries of freshwater trematodes (Trematoda, Digenea), thanks to the use of integrative taxonomic methods. The majority of digeneans (28 out of 41 known) were characterised with molecular genetic methods and morphological analyses, with some of their life-cycle stages and geographical distribution assessed. A surprising diversity has been discovered, comprising species of the families Allocreadiidae, Cyclocoeliidae, Diplostomidae, Echinostomatidae, Gorgoderidae, Plagiorchiidae, Notocotylidae, Schistosomatidae, and Strigeidae. Many of the recorded species complete their life cycles within Iceland, with three snail species (Ampullaceana balthica, Gyraulus parvus, Physa acuta) known as intermediate hosts. No trematodes endemic for Iceland were found; they appear to be generalists with wide geographical ranges dispersed mainly by migratory birds. Interestingly, fish trematodes recorded in Iceland were found in mainland Europe, indicating that they might be dispersed by anadromous fishes, by human activity, or by migratory birds carrying intermediate hosts. The trematode fauna is mainly Palaearctic, with few species recorded in North America. We highlight the ongoing need for precise species identification via integrative taxonomic methods, which is a baseline for any further ecological studies and adequate epidemiological and conservation measures. Also, there is still a need of obtaining well-preserved vouchers of adults for definite species delimitation.

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.