IDENTIFICATION AND PHYLOGENETIC ANALYSIS OF CHLOROMYXUM BRACHYCEPHALI N. SP. (MYXOZOA: CHLOROMYXUM) FROM THE GALLBLADDER OF LUCIOBARBUS BRACHYCEPHALUS IN CHINA

During a survey of myxosporean diversity in fishes from Hunan Province, China, a myxosporean infection was detected in the gallbladder of Luciobarbus brachycephalus. The morphological features were consistent with those of Chloromyxum species. Mature spores were spherical in the valvular view, measuring (14.7±0.7) (13.7—15.5) µm in length, (13.6±0.7) (12.4—14.4) µm in width, and (14.1±0.5) (13.6—14.9) µm in thickness. The sutural ridge was straight, and each valve possessed 10—11surface ridges. Four equal-sized pyriform polar capsules, located at the anterior end of the spore, occupied approximately one-third ofits length. These capsules measured (4.8±0.6) (4.0—5.7) µm in length and (3.7±0.7) (2.7—4.7) µm in width, each containing a polar filamentwith 5—6 coils. Morphological comparisons indicated that the present species differed from all previously described Chloromyxum species. BLAST analysis revealed that the present showed the highest sequence identity (95.14%) with Chloromyxum cristatum (AY604198), a value considerably lower than the commonly accepted threshold for intraspecific variation. Phylogenetic analysis indicated that the present species clustered with C. cristatum and C. auratum, forming a distinct subclade. These results support the polyphyletic group of Chloromyxum and suggest that host identity and infection site may play important roles in its evolutionary diversification. Furthermore, the caudal filaments may be relevant to species divergence within the genus. In conclusion, the parasite discovered from the gallbladder of L. brachycephalus represents a new species and designated as Chloromyxum brachycephali n. sp.