Helminths of the Antarctic dragonfish, Parachaenichthys charcoti (Perciformes, Notothenioidei, Bathydraconidae) Studied near Galindez Island (Argentine Islands, West Antarctica)

Infection patterns of helminth community in black rockcod Notothenia coriiceps in West Antarctica over a 6-year term

Patterns of the rockcod Notothenia coriiceps infection with helminths were analysed to understand the dynamics of parasite communities in this Antarctic fish and to test their stability over time. The study was performed using helminth samples collected from 183 N. coriiceps in 2014-2015 and 2020-2021 in the vicinity of the Ukrainian Antarctic station (UAS) "Akademik Vernadsky", Galindez Island, Argentine Islands, West Antarctica. Overall, 25 helminth taxonomical categories (nine trematodes, four cestodes, five nematodes, and seven acanthocephalans) were subjected to analysis. A direct comparison of the helminth population characteristics showed that nine species significantly changed their infection parameters during the 6 years between the samples. Seven of them (Pseudoterranova sp., Contracaecum sp., Ascarophis nototheniae, monolocular metacestodes, bilocular metacestodes, Metacanthocephalus rennicki, and Diphyllobothrium sp.) were found to have a significant impact on the differences between helminth infracommunities in 2014-2015 and 2020-2021. Most studied patterns of helminth component community appeared to show a stable tendency, and observed fluctuations were close to the steady trend. Slight but significant changes in the infection patterns observed in this study might have been caused by changes in the populations of intermediate, paratenic, and definitive hosts of helminths (marine invertebrates, mammals, and birds), which participate in helminth transmission in Antarctic ecosystems.

First morphological and molecular characterization of cystacanths of Corynosoma evae Zdzitowiecki, 1984 (Acanthocephala: Polymorphidae) from Antarctic teleost fishes

Cystacanths of the polymorphid acanthocephalan Corynosoma evae Zdzitowiecki, 1984 were examined and redescribed based on newly collected material from teleost fishes from coastal waters of the Galindez Island (Argentine Islands, West Antarctica). Detailed morphological data, measurements and photomicrographs, including scanning electron microscopy images, are presented. Our morphological and morphometrical analyses confirmed the validity of C. evae; however, three key characteristics of taxonomic importance (i.e., the number of rows of hooks on the proboscis, and the number and arrangement of genital spines in males) showed significant morphological variability. In addition, a genital spine in the posterior body end of a female is reported for the first time. This study provides the first sequences of the small and large subunits nuclear ribosomal RNA genes (SSU and LSU) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) for C. evae. Maximum likelihood and Bayesian inference analyses of the SSU + LSU + cox1 and the cox1 datasets placed C. evae as a sister lineage to a clade formed by C. validum Van Cleave, 1953 and C. villosum Van Cleave, 1953, although with low support. In contrast, the position of C. evae in the phylogenetic analysis of the SSU + LSU dataset remained unresolved. Finally, C. arctocephali Zdzitowiecki, 1984 from pinnipeds from the subantarctic and Antarctic regions is considered as a valid species.

Trematodes from Antarctic teleost fishes off Argentine Islands, West Antarctica: molecular and morphological data

In 2014-2015 and 2019-2021, teleost fishes off Galindez Island (Antarctic Peninsula) were examined for trematodes. Combined morphological and molecular analyses revealed the presence of eight trematode species of four families (Hemiuridae, Lecithasteridae, Opecoelidae, Lepidapedidae) from five fish species. Only adult trematodes were found and all of them are Antarctic endemics with their congeners occurring on other continents. The hemiuroids, Elytrophalloides oatesi (Leiper & Atkinson, 1914), Genolinea bowersi (Leiper & Atkinson, 1914), and Lecithaster macrocotyle Szidat & Graefe, 1967 belong to the most common Antarctic species and together with Lepidapedon garrardi (Leiper & Atkinson, 1914) and Neolebouria georgiensis Gibson, 1976 they were recorded as the least host-specific parasites. The originally sub-Antarctic Neolepidapedon macquariensis Zdzitowiecki, 1993 is a new record for the Antarctic Peninsula and Parachaenichthys charcoti (Vaillant), is a new host record. Neolebouria terranovaensis Zdzitowiecki, Pisano & Vacchi, 1993 is considered a synonym of N. georgiensis because of identical morphology and dimensions. The currently known phylogenetic relationships within the studied families are supported, including the polyphyly of Macvicaria Gibson & Bray, 1982 with the future need to accommodate its Antarctic species in a new genus. The validity of M. georgiana (Kovaleva & Gaevskaja, 1974) and M. magellanica Laskowski, Jezewski & Zdzitowiecki, 2013 needs to be confirmed by further analyses. Genetic sequence data are still scarce from Antarctica, and more studies applying integrative taxonomic approaches and large-scale parasitological examinations of benthic invertebrates are needed to match sequences of larval stages to those of well-characterised adults and to elucidate trematode life-cycles.