The characteristics of the infection of juvenile Atlantic salmon with glochidia of the freshwater pearl mussel in rivers of Northwest Russia

Abstract

-The decline of freshwater pearl mussel (Margaritifera margaritifera L.) populations is globally well documented, but there is a lack of knowledge concerning the status of the species and its interaction with host fishes in the rivers of the White and Baltic Seas. This study aimed to identify the host fish of pearl mussel in four rivers of Karelia (Northwest Russia), to analyse the duration of the parasitic phase, and the susceptibility of fish hosts to the infestation. Juvenile sea-migrating and land-locked Atlantic salmon (Salmo salar L.) were identified as the most important hosts. In the Keret' River, reduced numbers of juvenile Atlantic salmon are likely to result in a decline of pearl mussel. This problem does not appear to be present for the other three studied rivers. Pearl mussel glochidia were mostly found in yearlings (0+), whereas older fish were infected less, suggesting a more complex pattern of host use than commonly expected. The remote location of Karelian pearl mussel rivers, the high number of pearl mussels in them, and their rather pristine state all suggest that these rivers have a high conservation priority. The importance of Atlantic salmon as a host fish and the emerging declines of Atlantic salmon populations, e.g., in the Keret' River, suggest that the sustaining of this host species should have a high conservation priority. Key-words:Margaritifera margaritifera / Salmo salar / glochidial infestation / host fish Résumé -Les caractéristiques de l'infestation de saumons atlantiques juvéniles par des glochidies de la moule perlière d'eau douce dans les rivières de la Russie du Nord-Ouest. Le déclin des populations de la moule perlière (Margaritifera margaritifera L.) est globalement bien documenté, mais il y a un manque de connaissances concernant le statut de l'espèce et son interaction avec les poissons hôtes dans les rivières des mers Blanche et Baltique. Cette étude visait à identifier les poissons hôtes de la moule perlière dans quatre rivières de la Carélie (Ouest de la Russie), pour analyser la durée de la phase parasitaire, et la sensibilité des poissons hôtes à l'infestation. Les juvéniles de saumon atlantique migrants ou land-locked (Salmo salar L.) ont été identifiés comme les hôtes les plus importants. Dans la rivière Keret', la réduction du nombre de saumons atlantiques juvéniles est susceptible d'entraîner une baisse de la moule perlière. Ce problème ne semble pas être présent pour les trois autres rivières étudiées. Les glochidies de moule perlière ont été principalement trouvés dans les poissons de l'année (0+), tandis que les poissons plus âgés ont été moins infectés, ce qui suggère un modèle de l'utilisation des hôtes plus complexe que généralement prévu. L'éloignement des rivières de Carélie à moules perlières, le nombre élevé de moules perlières présentes, leur état plutôt vierge suggèrent que ces rivières ont une haute priorité de conservation. L'importance du saumon atlantique comme poisson hôte et les baisses en cours des populations de saumon de l'Atlantiqu...

Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) differ in their suitability as hosts for the endangered freshwater pearl mussel (Margaritifera margaritifera) in northern Fennoscandian rivers

“…However, Ieshko et al. () recently found that land‐locked Lake Ladoga (Baltic Sea drainage) salmon were hosts for FPM in a Russian river, but they did not find any brown trout for host comparison. In Norway, FPM populations parasitising only brown trout or salmon have been found in field surveys throughout the country (Karlsson et al., ).…”

Early stages of Margaritifera margaritifera glochidiosis in Atlantic salmon: Morphopathological characterization

“…This artefact may occur during fixation in well-developed larvae due to the high osmolarity of the fixative and the low diffusion coefficient of the periostracum, similar to other hard tissues, such as cartilage, eye and certain fish tissues (Margo & Lee, 1995;Nassar et al, 2015;Speilberg, Evensen, Bratberg & Skjerve, 1993). Therefore, an accurate evaluation of the integrity of parasite periostracum and internal structures is essential to distinguish this artefact from non-viable glochidia with altered morphology (Ieshko et al, 2016;Treasurer & Turnbull, 2000).…”

An alien fish threatens an endangered parasitic bivalve: the relationship between brook trout (Salvelinus fontinalis) and freshwater pearl mussel (Margaritifera margaritifera) in northern Europe

“…One apparent explanation for the incomplete knowledge is the occurrence of FPM in oligotrophic waters that are close to their natural state, meaning that many of the remaining populations are located in remote areas far from human civilization (see e.g. Ostrovsky and Popov 2011, Oulasvirta 2011, Varandas et al 2013, Ieshko et al 2016. Therefore, unexplored rivers and streams in such areas may harbour more unknown FPM populations vulnerable to possible environmental operations by man.…”

“…on the western coastline of the Baltic Sea, is known to exclusively parasitize salmon. However, in a Russian river, land-locked salmon from Lake Ladoga (Baltic Sea drainage) was recently found to serve as host for FPM, but the suitability of brown trout as FPM hosts in that river is unknown (Ieshko et al 2016). Outside the Baltic area, Hastie and Young (2001) observed higher infectivity of FPM in salmon than in brown trout in several Scottish rivers, and Karlsson et al (2014) found many Norwegian FPM populations to be exclusively adapted to use only either salmon or brown trout as their host.…”