Beschreibung:
<jats:title>Abstract</jats:title><jats:sec><jats:title>Objective</jats:title><jats:p>Myxosporidiosis of bagrid fishes has been a focus of aquaculture research in recent years. The purpose of this study is to characterize a novel myxobolid, named <jats:italic>Myxobolus xiushanensis</jats:italic> n. sp., infecting Yellowhead Catfish <jats:italic>Tachysurus fulvidraco</jats:italic> in China.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We used molecular biology, morphology, phylogeny, and histopathology in the present study.</jats:p></jats:sec><jats:sec><jats:title>Result</jats:title><jats:p>Mature myxospores were circular to ellipsoidal in valve view, measuring 12.2 ± 0.4 μm (mean ± SD; range = 11.2–13.2 μm) in length and 10.6 ± 0.4 μm (9.5–11.1 μm) in width. Two oval polar capsules were equal in width (3.4 ± 0.2 μm; 3.0–3.8 μm) but slightly unequal in length: 5.6 ± 0.3 μm (5.3–6.1 μm) and 4.7 ± 0.2 μm (4.4–5.5 μm). The polar capsule was packed with five to seven spirals of polar tubules. Histopathological investigation demonstrated that the plasmodium under the cuticular layer of the gill arch only induced a local inflammatory response and did not cause serious damage to the gill arch's internal structure. The two small subunit (SSU) ribosomal DNA sequences of <jats:italic>M. xiushanensis</jats:italic> n. sp. showed 100% similarity and uniqueness, and the highest similarity with other myxosporean sequences in GenBank was 90.27% (query coverage = 94%). The secondary structures of the SSU ribosomal RNA revealed that the present species was distinctly different from related species in regions V4 and V7. Phylogenetic analysis showed that <jats:italic>M. xiushanensis</jats:italic> n. sp. clustered independently within a branch.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>These results enrich our understanding of the biodiversity of myxobolids infecting bagrid fishes and provide fundamental data for the diagnosis of myxosporidiosis.</jats:p></jats:sec>