Morphological and molecular characterization of a new myxosporean species, Myxidium hangae n. sp. (Myxozoa: Myxosporea), infecting the gallbladder of the freshwater armorhead catfish Cranoglanis bouderius (Richardson) (Siluriformes: Cranoglanididae) in northern Vietnam.

During a survey of myxosporean parasites in freshwater fishes from northern Vietnam conducted between 2018 and 2026, myxospores were observed in the gallbladder of Cranoglanis bouderius (Siluriformes: Cranoglanididae). The parasite was detected in two of 35 examined hosts (5.7%). Mature myxospores are fusiform, measuring 11.1-12.7 μm long, 5.1-5.6 μm wide, and 4.5-4.9 μm thick. The myxospores consist of two valves joined along a sutural line, each valve bearing 7-8 longitudinal grooves. Two equal-sized pyriform polar capsules are located at opposite ends of the myxospore, measuring 3.0-3.9 μm long by 2.3-3.4 μm wide, each containing a polar tubule with 4-5 coils. Molecular analysis based on SSU rDNA sequence data revealed that the present species is genetically distinct from other myxosporean species with available sequence data. The combination of morphological features and molecular evidence supports the description of Myxidium hangae n. sp. This study represents the first record and description of a species of Myxidium from the fish fauna of Vietnam and contributes to current knowledge of myxosporean diversity in Southeast Asia.