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Diseases of Aquatic Organisms

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DAO 148:29-41 (2022)  -  DOI:

Vannella mustalahtiana sp. nov. (Amoebozoa, Vannellida) and rainbow trout nodular gill disease (NGD) in Russia

Alexander Kudryavtsev1,#, Aleksey Parshukov2,#,*, Ekaterina Kondakova3,4, Ekaterina Volkova1

1Laboratory of Cellular and Molecular Protistology, Zoological Institute, Russian Academy of Sciences, 199034 Saint Petersburg, Russia
2Institute of Biology, Karelian Research Centre, Russian Academy of Sciences, 185910 Petrozavodsk, Russia
3Saint Petersburg State University, 199034 Saint Petersburg, Russia
4Saint Petersburg branch of the Russian Federal Research Institute of Fisheries and Oceanography «VNIRO» (L.S. Berg State Research Institute of Lake and River Fisheries), 199053 Saint Petersburg, Russia
*Corresponding author:
#These authors contributed equally to this work

ABSTRACT: An outbreak of nodular gill disease (NGD) in farmed rainbow trout Oncorhynchus mykiss (Walbaum, 1792) was recorded in Ladoga Lake (Karelia, north-western Russia) in Spring 2020. The disease was characterised by typical clinical signs including asphyxiation, distended opercula, loss of activity and swimming upside down under the water surface. Maximum monthly mortality was 15.2%. The histological examination of the gills showed deformation and clubbing of lamellae, epithelial hypertrophy and hyperplasia, lamellar fusion and fusion of filaments. Granulomas were located within the epithelial layer and/or rose above its surface. Light microscopic in vivo observations of the mucus smears from the affected gills revealed numerous amoeboid protists demonstrating a flattened body when adhering to the substratum, and blunt, radiating pseudopodia when afloat. Based on these morphological characters, these amoebae could be assigned to the Discosea (Amoebozoa), and analyses of their small subunit rRNA gene sequences showed that they belonged to the genus Vannella Bovee, 1965. The results reported herein support the designation of a new species, V. mustalahtiana sp. nov. Despite having been isolated from the gills of a freshwater fish, the species belongs to a clade of Vannella comprising mostly species isolated from marine and brackish water habitats. These findings may be essential for the aetiology and treatment of the disease.

KEY WORDS: Lobose amoebae · Nodular gill disease · Rainbow trout · Oncorhynchus mykiss · Freshwater

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Cite this article as: Kudryavtsev A, Parshukov A, Kondakova E, Volkova E (2022) Vannella mustalahtiana sp. nov. (Amoebozoa, Vannellida) and rainbow trout nodular gill disease (NGD) in Russia. Dis Aquat Org 148:29-41.

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