Remarks on the validity of Myxobolus ampullicapsulatus and Myxobolus honghuensis (Myxozoa: Myxosporea) based on SSU rDNA sequences

In the present study, we isolated three populations of Myxobolus ampullicapsulatus from the gills of crucian carp, Carassius auratus auratus, two from Yongchuan, Chongqing area and one from Poyang Lake, Jiangxi area, China, sequenced their complete small subunit ribosome RNA gene, analyzed their genetic distance and gene similarity, and explored their relationship based on Bayesian inference and maximum likelihood analyses of their small subunit ribosomal DNA. The results combined with their morphological characteristics suggest that M. ampullicapsulatus infecting the gills and pharynx of allogynogenetic gibel carp, Carassius auratus gibelio, should be Myxobolus honghuensis. This study highlights the importance of DNA sequence comparisons for distinguishing Myxobolus species and indicates that the intra-species identification for the two Myxobolus species mentioned in the present research should be less than ten variation sites. In morphology, M. honghuensis Liu et al. (2012) parasitic on the gills of C. auratus auratus (goldfish) was collected from Chongqing area, and its mature spore was 16.5-19.5 × 8.5-10.0 μm in size, polar capsule was 7.0-10.0 × 2.5-4.0 μm in size, and polar filament had 9-10 coils. M. honghuensis Liu et al. (2012) isolated from the pharynx of C. auratus gibelio was sampled in Hubei area, and its mature spore was 15.1-19.5 × 9.0-11.3 μm in size, polar capsule was 7.9-8.1 × 3.0-4.5 μm in size, and polar filament had 7-8 coils.