Identification and Characterization of Myxobolus pronini (Cnidaria: Myxozoa) from Gibel Carp Carassius auratus gibelio and Goldfish C. auratus: New Fish Host, Infection Site, and Geographic Distribution in China

Myxozoans represent a significant group of parasitic pathogens affecting both wild and farmed fish. For accurate and comprehensive early detection, the composition of myxozoan pathogens in fish has consistently been a primary focus for parasitologists. In China, we undertook an investigation into myxozoan infection in fish from Shandong Province, China, successfully isolating a myxozoan species from gibel carp Carassius auratus gibelio Bloch, 1782 and goldfish C. auratus Linnaeus, 1758. In the present study, this myxozoan species was identified by detailed morphological and molecular analysis. This parasite is characterized by the presence of visible plasmodia in various organs (intestine, liver, gallbladder, and abdominal cavity) of gibel carp as well as the abdominal cavities of goldfish. In comparison to all documented myxozoan species, this myxozoan species exhibits morphological identity with Myxobolus pronini Liu, Batueva, Zhao, Zhang, Zhang, Li, Li, 2016, in terms of spore morphology. Molecular sequence analysis, including sequence similarity, variable site, and the secondary structure of SSU rRNA, indicates that the present myxozoan species closely resembles M. pronini. Furthermore, phylogenetic analyses revealed that all isolates collected from different organs and hosts in this study clustered with M. pronini, forming a distinct branch within the Carassius-infecting clade. Consequently, the present myxozoan species can be confidently identified as M. pronini. Compared with the previous reports on M. pronini, this study documents, for the first time, goldfish as a host, intestines and gallbladders as the sites of infection, and Shandong Province as the geographic distribution of this myxozoan species.