Myxobolus linzhiensis n. sp. (Myxozoa: Myxobolidae) from the gill filament of Schizothorax oconnori Lloyd (Cyprinidae: Schizothoracinae) in Tibet, China: morphological and molecular characterization.

In this report, a new myxosporean species, Myxobolus linzhiensis n. sp. (Cnidaria: Myxozoa: Bivalvulida), was described from the endemic cyprinid Schizothorax oconnori inhabiting the Yarlung Tsangpo River in the Tibetan plateau, China. The whitish ellipsoidal plasmodia of M. linzhiensis n. sp. grew under the epithelium of gill filaments, 1.7-mm long and 0.4-mm wide, and were found in the 3 of 8 examined S. oconnori (37.5%). Mature spores appeared suborbicular in frontal view, fusiform shaped in lateral view with tapering anterior, measuring 11.4 ± 0.7 (10.1-13.0) μm in length, 10.6 ± 0.4 (10.0-11.3) μm in width, and 6.6 ± 0.3 (6.2-7.0) μm in thickness. Two equal polar capsules were pyriform with an apophysis at its top end, measuring 5.7 ± 0.5 (4.8-6.7) μm in length, 3.8 ± 0.2 (3.2-4.2) μm in width, and polar filaments coiled 4 turns. Spore valves were symmetrical, and sutural ridge was straight and thin, running near the middle of the valves. Although Myxobolus linzhiensis n. sp. showed similar morphological characteristics with Myxobolus chushi Dar Kaur & Chishti 2017 from Schizothorax niger, Myxobolus kienweiensis Ma, 1976 from Schizothorax davidi, the new myxosporean was distinguished with them in spore shape, polar filament, and host-tissue tropism. Homology search by BLAST in GenBank indicated that the obtained 18S rDNA sequence of M. linzhiensis n. sp. (KY965935) did not match any available myxozoan sequence, most similar to Henneguya zikaweiensis, and showing less than 93% sequence similarity. Phylogenetical analyses demonstrated that M. linzhiensis n. sp. was firmly clustered in the clade consisting of myxosporeans Thelohanellus, Myxobolus, Henneguya from Asian cyprinids. This study is the first report on myxosporean parasitizing in endemic fish in the Tibetan Plateau, China.