New record of gill hemorrhagic parasite Myxobolus richardsonii n. sp. (Cnidaria: Myxozoa) infecting Schizothorax richardsonii in Kashmir Himalayas

Myxozoans are highly specialized metazoan parasites with a very diverse host range that live on aquatic hosts. In both wild and farm-raised fish, myxozoans are the most frequent parasites. The aim of the current study was to evaluate any myxozoan parasite found in different organs of Schizothorax richardsonii. Live fish were transported with artificial aeration to the University of Kashmir. Thirty-five fish specimens were examined during the study period, and only gills of 6 fish were determined to be infected. Taxonomic study was carried out with the help of different keys, and histopathologcal study was assayed in order to study the diseased organs of the fish. Besides, characterization of partial 18S rDNA gene was also done in the present study as per the standard procedures. The findings showed that the plasmodia were big, oval shaped, and white in color, measuring 1.5 × 2.0 mm. They were referred to as intralamellar vascular-type plasmodia (LV3). Histological changes in the gills included inflammation, gill epithelium lifting, hypertrophy of lamellar cells, and fusion of nearby gill lamellae. The myxospore body had a tiny ICP at the anterior end and was spherical to ovoidal in form, measuring 11.19 × 7.66 µm. Polar tubules were pyriform in shape and measuring 6.12 × 1.95 µm, having coils up to 7 in number. The gill plasmodium index showed a moderate level of infection (GPI 2). According to their phylogenetic relationships, M. richardsonii n. sp. was sister species to Myxobolus sp. KLT and Myxobolus dermiscalis–infecting scales of Labeo rohita from Myanmar and India, respectively. The novel sequence KU885918 and 30 additional sequences from closely related sequences showed 97% homogeneity or above in NCBI GenBank database. Moreover, the tree showed grouping based on the tissue tropism, host, and geographical location of the infected host. Morphological, histological, and molecular characterizations were used to identify a novel myxosporean parasite, Myxobolus richardsonii n. sp. in cold water fish, Schizothorax richardsonii (Heckel), obtained from Wullar Lake in Kashmir Himalayas, India. © 2023, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.