We describe an unusually high infection rate of Gyrodactylus salaris Malmberg in juvenile Atlantic salmon Salmo salar L. of Baltic Sea origin, which are generally believed to be more resistant to G. salaris than East Atlantic salmon populations. Based on analyses of mitochondrial (complete cytochrome oxidase 1 [CO1] gene, 1548 bp) and nuclear (ADNAM1, 435 bp; internal transcribed spacer [ITS] rDNA region, 1232 bp) DNA fragments, the closest relatives of the characterized Estonian G. salaris strain were parasites found off the Swedish west coast and in Raasakka hatchery, Iijoki (Baltic Sea, Finland). Analyses of 14 microsatellite loci of the host S. salar revealed that approximately 40% of studied fish were triploids. We subsequently identified triploid Atlantic salmon of Baltic origin as more susceptible to G. salaris infection than their diploid counterparts, possibly due to compromised complement-dependent immune pathways in triploid salmon. This is in accordance with earlier studies that have shown elevated susceptibility of triploids to various viral or bacterial pathogens, and represents one of the first reports of increased susceptibility of triploid salmonid fish to an ectoparasite. However, further experimental work is needed to determine whether triploid Atlantic salmon is generally more susceptible to G. salaris compared to their diploid counterparts, irrespective of the particular triploidization method and population of origin. KEY WORDS: Atlantic salmon · Gyrodactylus salaris · Pathogen susceptibility · Triploid · Microsatellites · Baltic Sea Resale or republication not permitted without written consent of the publisherDis Aquat Org 91: [129][130][131][132][133][134][135][136] 2010 tect significant differences in susceptibility between diploid and triploid fish. For example, both diploid and triploid rainbow trout exposed to Vibrio ordalii, Aeromonas salmonicida, or infectious hematopoietic necrosis virus demonstrated similar mortality rates (Yamamoto & Iida 1995). Similar mortality rates between diploid and triploid Atlantic salmon were also observed after experimental infection with Renibacterium salmoninarum (Bruno & Johnstone 1990).Gyrodactylosis is a parasitic disease of salmonid fishes caused by the viviparous ectoparasite monogenean flatworm Gyrodactylus salaris, which belongs to the G. wageneri species-group, of the subgenus Limnonephrotus (family Gyrodactylidae, Malmberg, 1957). Due to 'hyperviviparity' (also known as a 'Russian doll' style of reproduction), combined with a rapid generation time, it reproduces fast, and in a matter of weeks a single worm can produce thousands of progeny , Buchmann 2008. G. salaris damages fish not only by consuming mucus and epithelial cells of the host but also by piercing the fish epithelium with its hooklets, compromising its osmoregulatory function, and leaving it vulnerable to fungal and bacterial infections. Importantly, Atlantic salmon populations exhibit marked differences in susceptibility to G. salaris infection, with populations fr...

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-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...

A new species, Caudotestis dobrovolski n. sp., is described from Liparis sp. (Scorpaeniformes: Liparidae) and Eumicrotremus fedorovi Mandrytsa, 1991 (Scorpaeniformes: Cyclopteridae), caught in the Simushir Island area of the North Pacific. This species differs from six previously known congeners by the following combination of features: the excretory vesicle reaches to the anterior edge of the ventral sucker, uterus pretesticular, genital pore prebifurcal and median, and testes entire or with irregular outline, occasionally distinctly lobate. Phylogenetic analysis of 28S rRNA gene partial sequences suggests a sister position of Caudotestis Issaitschikov, 1928 to the genus Biospeedotrema Bray, Waeschenbach, Dyal, Littlewood, & Morand, 2014, and unites C. dobrovolski n. sp. + Biospeedotrema spp. with Zdzitowieckitrema incognitum Sokolov, Lebedeva, Gordeev, & Khasanov, 2019. The phylogenetic relationship of Biospeedotrema and Zdzitowieckitrema Sokolov, Lebedeva, Gordeev, & Khasanov, 2019 with respect to the Opecoelidae is currently uncertain and, within the Xiphidiata, these genera are currently without adequate familial classification. However, Caudotestis belongs to the Stenakrinae, a subfamily within the Opecoelidae. Three other stenakrine species—Holsworthotrema enboubalichthys Martin, Huston, Cutmore, & Cribb, 2018, Holsworthotrema chaoderma Martin, Huston, Cutmore, & Cribb, 2018, and Scorpidotrema longistipes Aken’Ova & Cribb, 2003—are integrated into a large clade of the opecoelid trematodes. Therefore, the Stenakrinae is apparently polyphyletic.

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