Morphological variation in Myxobolus drjagini (Akhmerov, 1954) from silver carp and description of Myxobolus paratypicus n. sp. (Cnidaria: Myxozoa)
There is uncertainty in the identification of Myxobolus drjagini, the causative agent of silver carp twist disease, in the literature. An investigation of fish parasites in Lake Taihu, China, revealed several Myxobolus drjagini–like myxosporeans infecting the subcutaneous tissue of the head skin, the olfactory and oculomotor nerves in the cranial cavity, and the intrafilamental epithelium of the gills of silver carp Hypophthalmichthys molitrix (Valenciennes, 1844). Myxospores from the head skin and the nerves were identified as conspecific to M. drjagini based on morphological and molecular data; although the spores from each of the two organs presented morphological variations. SSU rDNA sequence analysis revealed that the sequence of M. drjagini previously deposited in GenBank (AF085179) was invalid. Myxospores from the gills were identified as Myxobolus paratypicus n. sp. The spores were oval, asymmetric in frontal view, 13.8 (12.9–14.9) μm long, 9.9 (9.2–11.1) μm wide, and 7.0 μm thick. Two pyriform polar capsules were unequal in size (ratio above 4:1) with slightly converging anterior ends, and the posterior end of the large polar capsule extended beyond the middle of the spore. The large polar capsule was 7.5 (6.2–8.2) μm long and 5.0 (4.2–5.6) μm wide; the small polar capsule was 2.7 (2.1–3.6) μm long and 1.4 (1.1–1.9) μm wide. Polar filaments were coiled with 7–8 turns in the large polar capsule. The SSU rDNA sequence of M. paratypicus n. sp. was not identical to that of any myxozoan available in GenBank and showed highest similarity with M. drjagini (96%) and Myxobolus pavlovskii (95%) collected from bighead carp and silver carp, respectively.
KeywordsMyxozoan Myxobolus Silver carp Brain SSU rDNA
Authors thank Kai Chen and Sheng-Chen Liao, for providing support in the sample collections.
This work was financially supported by the Central Public-interest Scientific Institution Basal Research Fund, CAFS (2017HY-ZD1008), the Natural Sciences Foundation of Jiangsu (BK20171152), the Natural Sciences Foundation of China (31572662), and the earmarked fund for China Agriculture Research System (CAR–45).
Compliance with ethical standards
Animal experiments were approved by the Ethical Committee of the Freshwater Fisheries Research Center and followed the national guidelines for the care and use of vertebrate animals.
Conflict of interest
The authors declare that they have no conflict of interest.
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