Molecular and phylogenetic characterization of Thelohanellus qadrii (Myxozoa, Myxosporea, Bivalvulida) infecting the secondary gill epithelium of Indian major carp, Catla catla (Hamilton, 1822)

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Myxosporean taxonomy which is traditionally based on the morphology of the myxospore stage, is in a state of flux given new insights provided by the expanding dataset of DNA sequences. To date, more than 40 species of Thelohanellus from India have been described according to morphometric characteristics. Nevertheless, molecular data on these histozoic myxosporean parasites of freshwater fish are scarce. In the present study, molecular characterizations of Thelohanellus qadrii infecting the secondary gill epithelium of Indian major carp Catla catla (Hamilton, 1822) and its phylogenetic relationship is reported. The sub-adult cultured catla were observed to have low to moderate gill myxosporean infections. The morphometry of mature spores was in compliance with original descriptions of T. qadrii. Based on the analysis of 18S rRNA gene, phylogenetic clusters which were established according to a consensus sequence, illustrated the taxonomic placement of a series of myxobolids. The DNA sequence homogeneity of T. qadrii (KF170928) with other Thelohanllus spp. ranged from 78% to 95% and formed a dichotomy with cyprinid gill lamellae infecting T. toyamai (HQ338729). Distance matrix results indicated a high genetic diversity among myxosporeans. The present report is the first on the molecular and phylogenetic characterizations of T. qadrii.