Žiobrių (Vimba vimba) ir vėjažuvių (Belone belone) parazitologinis tyrimas skirtingose vandens ekosistemose
Venslovaitė, Margarita |
Migruojančios žuvys Lietuvoje turi didelę ekonominę bei ekologinę reikšmę. Tačiau migracijos metu jos patiria didžiulį stresą, dėl kurio silpnėja imunitetas bei atsparumas ligoms ir parazitams. Parazitai eikvoja šeimininko energijos atsargas, trikdo mitybą, aplinkos jutimą ar sukelia žuvies morfologinius pokyčius, ir visa tai neigiamai veikia vertingų žuvų išteklius. Visgi, Lietuvoje trūksta išsamių tyrimų apie migruojančių žuvų parazitų įvairovę skirtingose vandens ekosistemose. Todėl darbo tikslas yra nustatyti žiobrio (Vimba vimba) ir vėjažuvės (Belone belone) parazitų įvairovės ir bendrijų struktūros ypatumus skirtinguose gyvenimo ciklo etapuose skirtingose vandens ekosistemose. 2024 m. žiobriai buvo sugauti: Salanto upėje (n=13), Kuršių mariose (n=30) ir Baltijos jūroje (n=30), o vėjažuvės – Baltijos jūros priekrantėje (n=30). Kiekviena žuvis buvo užšaldoma ir vėliau laboratorijoje parazitologiškai tiriama. Rasti parazitai buvo identifikuojami morfologiniais arba genetiniais rūšių atpažinimo metodais. Tyrimo metu buvo identifikuota mažiausiai 19 parazitų rūšių, priklausančių šešioms sistematinėms grupėms: Monogenea – 3, Digenea – 7, Nematoda – 4, Cestoda – 3, Acanthocephala – 1 ir Crustacea – 1. Jūros žiobrių ir vėjažuvių parazitų bendrijos statistiškai skiriasi struktūra ir rūšine įvairove. Tuo tarpu žiobrių parazitų bendrijos sudėtis migracijos metu didėja: mažiausia jauniklių Salante, didžiausia besimaitinančiųjų Baltijos jūroje. Pirmą kartą Lietuvos priekrantėje sugautose vėjažuvėse aptikta antrinė rūšis – monogeninė siurbikė Axine belones (P=50%, mI=3), būdinga Atlanto vandenyne gyvenančioms žuvims. Šis rezultatas patvirtina spėjimus, kad suaugusios vėjažuvės į Baltijos jūrą migruoja iš Atlanto vandenyno ar Šiaurės jūros. Išanalizavus žiobrių monogeninių siurbikių Paradiplozoon sp. morfologiją, galimų deformacijų, kaip aplinkos kokybės indikatoriaus, tyrimo metu nenustatyta. Šio tyrimo metu pirmą kartą Lietuvoje pritaikytas parazitų įvairovę grįstas aplinkos būklės indeksas, kurį, sukaupus daugiau duomenų apie pagrindinių žuvų parazitologinę situacija, galima plėsti vandens sistemų funkcionavimo ir biologinės įvairovės vertinimui.
Animal migration is a complex phenomenon during which individuals travel long distances encountering dynamic environmental conditions and numerous survival challenges: abiotic stressors, anthropogenic barriers (e.g., dams, pollution), and, therefore, heightened vulnerability to predation, diseases, and parasites. Parasites can exploit the energetic reserves of their fish hosts, disturb their feeding efficiency, sensory abilities, and induce morphological changes that increase their susceptibility to predators. In Lithuania, migratory fish like salmon, smelt, river lampreys, vimba and some others have significant ecological, economic, and cultural importance for coastal fisheries. Despite their importance, there is a notable lack of detailed parasitological studies on migratory fish in Lithuania, especially regarding parasite diversity and community structure across different aquatic habitats. This study aimed to investigate the diversity and structure of parasite communities infecting the migratory vimba (Vimba vimba) and garfish (Belone belone) during different migration phases. Vimba were sampled in the Salantas River (spawning grounds), the Curonian Lagoon (migration corridor), and the coastal zone of the Baltic Sea (feeding grounds), while garfish were collected from the Baltic Sea coast. Fish were collected using species and habitat appropriate methods: electrofishing in the river, traps in the lagoon, and nets in the sea. Each specimen was individually packed and frozen. A total of 103 fish were analyzed parasitologically: 73 vimba and 30 garfish. Parasitological dissections involved external and internal examinations, including eyes, gills, liver, heart, intestine, and swim bladder. Parasites were identified using morphological methods and molecular methods. The dual use of acetic carmine staining and glycerin mounting allowed for better visualization of diagnostic features across different parasite taxa. Moreover, the integration of molecular diagnostics helped overcome challenges caused by phenotypic plasticity, particularly in Diplostomum genus and nematodes. In total 3 088 parasites were found. 2 935 were found in vimba and 153 – in garfish. At least 19 parasite species were identified across six taxonomic groups: Monogenea (3), Digenea (7), Nematoda (4), Cestoda (3), Acanthocephala (1) and Crustacea (1). Three species of Diplostomum (D. mergi, D.spathaceum, and D. pseudospathaceum) and nematodes Anisakis simplex and Contracaecum rudolphi were confirmed using genetic methods. Nonmetric multidimensional scale analysis showed that parasite communities differed both in different fish species and among different vimba‘s life stages. Garfish‘s and vimba‘s parasites were completely different, while in vimba, parasite diversity and infection levels increased along the migration: from the river (lowest diversity) to the sea (highest diversity). This trend suggests an accumulation of parasites during migration, likely due to higher diversity and longer exposure to intermediate hosts. The presence of Tylodelphys clavata, Diplostomum pseudospathaceum, Tetracotyle sp. and Paradiplozoon spp. was common across all habitats, while certain parasites like Caryophyllaeus laticeps were restricted to the Baltic Sea site. Importantly, no structural abnormalities were observed in Paradiplozoon spp. (n=157) specimens. Moreover, measurements of Paradiplozoon body size confirmed findings in the literature, indicating that parasite size varies according to the size of the host. For the first time, the monogenean Axine belones in significant rates (P=50%, mI=3) was found on the gills of garfish caught in Lithuania supports the oceanodromous nature of the host. A. belones is known to infect garfish and other oceanic species on the Atlantic coast and in the North Sea. So far in the Baltic Sea, it has been found furthest at the coast of Germany. Star plot diagrams were applied to characterize environmental health using heteroxenous parasites and various ecological indices such as Shannon Diversity index, Simpson Dominance index, Berger-Parker index, and Pielou Evenness index. It reflects the ecological complexity and availability (diversity) of intermediate hosts across habitats. When interpreting star plot, it is important to keep in mind that environmental conditions may be influenced not only by anthropogenic impacts but also by natural environmental factors, therefore the best approach is to apply this method to compare the same type of habitats. This study represents the first application of parasite-based indicators to assess environmental condition in Lithuanian aquatic ecosystems. The findings confirm that parasite communities reflect both host ecology and environmental health, supporting their use as bioindicators. Also, this study represents one of the first modern parasitological assessments of migratory fish in Lithuanian waters, offering updated data on vimba‘s parasitological situation. Understanding host parasite dynamics in different aquatic ecosystems will become increasingly important for biodiversity protection, fisheries sustainability, and environmental policy under changing climate conditions.