Morphological, histopathological and molecular characterization of Myxobolus szekelyianus n. sp. (Cnidaria: Myxosporea: Myxobolidae) causing acute gill disease in Schizothorax esocinus (Heckel, 1838) from River Jhelum of Kashmir Himalayan region, India.

During the present study, we describe a novel myxozoan that forms plasmodia in the gill filament of Schizothorax esocinus collected from River Jhelum of Kashmir Himalayan region (n = 26). Description of the new species is based on morphology of the myxospore and on partial 18S rDNA gene. The results showed that the plasmodia were large, visible with naked eye, elongate in shape, whitish in colour, 8mm in diameter, at the centre of gill filament, histozoic, single or two in number per gill, but too big in size and filled by 1,000-1,400 myxospores. The myxospores measure 13.4 (length) x 9.5µm (width), short oval in frontal view, blunt at both in anterior and posterior, but somewhat narrowing towards the posterior end. Shell valves measure 0.45µm in thickness. No parietal folds were recorded. Two polar capsules equal in size, pyriform in shape were measured 7.3 x 4.2 µm (L x W). T he 18S r DNA o f this species (accession number MK785257) clustered phylogenetically with other related myxozoan parasites and showed maximum homogeneity of 98.63% with M. sp. SKBU-RC1 (MK412937) and M. sp. SKBU-RC2 (MK412937) infecting gills of Labeo rohita from India followed by 92.51% with M. pronini (MH329619) infecting abdominal cavity of Carassius gibelio from China. The study of histopathological changes of the gills revealed hypertrophy, hyperplasia, uplifting of cellular elements and severe damage to gill filaments resulting in suffocation of fish. By its unique myxospore morphology and its 18S rDNA sequence, we propose naming this species as Myxobolus szekelyianus n. sp [ABSTRACT FROM AUTHOR]