Identification of a new species of Gyrodactylus von Nordmann, 1832 (Monogenoidea Gyrodactylidae) isolated from Diptychus maculatus in Yarkand River, Xinjiang, China.

To investigate Gyrodactylus infection of fish in the river system of Xinjiang (China), Gyrodactylus individuals were isolated from specimens of Diptychus maculatus. Morphological characterization and phylogenetic analysis based on ITS1-5.8S-ITS2 rDNA locus revealed that the gyrodactylids belong to new species. Gyrodactylus diptychi n. sp. differs significantly in the morphology of the haptoral structures from 12 known species of Gyrodactylus found in fishes of the subfamily Schizothoracinae. In particular, G. diptychi n. sp. has a relatively short dorsal bar with thick and large ends, flat and straight hamuli roots, and small ventral bar processes. Furthermore, G. diptychi n. sp. is the only representative of Gyrodactylus found on D. maculatus. Using the BLASTn search of ITS1-5.8S-ITS2 rDNA sequences in GenBank and the Bayesian Information and Maximum Likelihood methods, we constructed phylogenetic trees for G. diptychi n. sp. As a result, our studies clearly identified that G. diptychi n. sp. was the first Gyrodactylus monogenean isolated from D. maculatus and a new species belonged to the subgenus Limnonephrotus.

New species of Gyrodactylus von Nordmann, 1832 (Monogenoidea: Gyrodactylidae) from Gymnodiptychus dybowskii (Kessler, 1874) (Schizothoracinae) in the Kunes River (Yili River basin), China.

Yili River system hosts a diverse fauna of fishes and parasites. Gymnodiptychus dybowskii is a rare and endangered aboriginal cold-water fish inhabit in the Yili river system. Our research identified a new species Gyrodactylus gymnodiptychi n. sp. isolated from G. dybowskii in the Kunes River (Yili River, China). Morphological comparison revealed identifiable differences between the new species and other parasites, including Gyrodactylus aksuensis, and Gyrodactylus tokobaevi, which are two known parasites living in G. dybowskii inhabit in the Aksu River west of Frunze (Kyrgyzstan), as well as Gyrodactylus montanus living in Shizothorax intermedius inhabited in the Tadzhikistan or Uzbekistan. Especially, the dorsal bar of G. gymnodiptychi n. sp. was raised at both ends with a hollow, and its hamulus roots were curved inward. The BLASTN search of GenBank did not detect any other ITS1-5.8S-ITS2 rDNA sequences same as G. gymnodiptychi's. Using the Bayesian Information and Maximum Likelihood methods to analyze the ITS1-5.8S-ITS2 rDNA gene sequences, we constructed phylogenetic trees for G. gymnodiptychi n. sp. Accordingly, our morphological and molecular research indicated that G. gymnodiptychi n. sp. was not only a new species of parasites but also the first Gyrodactylus member identified in the Yili River in China.

The complete mitochondrial genomes of the Leuciscus baicalensis and Rutilus rutilus: A detailed genomic comparison among closely related species of the Leuciscinae subfamily.

Cyprinidae is the largest family in the order of freshwater fish Cypriniformes. Increased subfamily members of Cyprinidae have been suggested to be re-classified for decades. In this study, we sequenced the mitochondrial genomes (mitogenomes) of Leuciscus baicalensis and Rutilus rutilus collected from northwest China and compared with other closely related species to determine their associated family or subfamily. We used Illumina NovaSeq to sequence the entire mitochondrial genomes of Leuciscus baicalensis and Rutilus rutilus and characterized the mitogenomes by the gene structure, gene order, and the secondary structures of the 22 tRNA genes. We compared mitogenome features of Leuciscinae with other subfamilies in Cyprinidae. We used the analytic Bayesian Information and Maximum Likelihood methods to determine phylogenetic trees of 13 PCGs. The mitogenomes of Leuciscus baicalensis and Rutilus rutilus were 16,607 bp and 16,606 bp, respectively. Organization and location of these genes were consistent with already studied Leuciscinae fishes. Synonymous codon usage was conservative in Leuciscinae as compared with other subfamilies in Cyprinidae. Phylogenetic analysis indicated that Leuciscinae was a monophyletic group, and genus Leuciscus was a paraphyletic group. Our approach, for the first time, of studying comparative mitochondrial genomics and phylogenetics together provided a supportive platform to the analysis of population genetics and phylogeny for Leuciscinae. Our results indicated a promising potential of comparative mitochondrial genomics in the manifestation of phylogenetic relationships between fishes, leading us to a suggestion that mitogenomes should be routinely considered in clarifying phylogenetics of family and subfamily members of fish.

Mitochondrial phylogenomics provides conclusive evidence that the family Ancyrocephalidae is deeply paraphyletic.

BACKGROUND: Unresolved taxonomic classification and paraphyly pervade the flatworm class Monogenea: the class itself may be paraphyletic and split into Polyopisthocotylea and Monopisthocotylea; there are some indications that the monopisthocotylean order Dactylogyridea may also be paraphyletic; single-gene markers and some morphological traits indicate that the family Ancyrocephalidae is paraphyletic and intertwined with the family Dactylogyridae. METHODS: To attempt to study the relationships of Ancyrocephalidae and Monopisthocotylea using a phylogenetic marker with high resolution, we sequenced mitochondrial genomes of two fish ectoparasites from the family Dactylogyridae: Dactylogyrus simplex and Dactylogyrus tuba. We conducted phylogenetic analyses using three datasets and three methods. Datasets were ITS1 (nuclear) and nucleotide and amino acid sequences of almost complete mitogenomes of almost all available Monopisthocotylea mitogenomes. Methods were maximum likelihood (IQ-TREE), Bayesian inference (MrBayes) and CAT-GTR (PhyloBayes). RESULTS: Both mitogenomes exhibited the ancestral gene order for Neodermata, and both were compact, with few and small intergenic regions and many and large overlaps. Gene sequences were remarkably divergent for nominally congeneric species, with only trnI exhibiting an identity value > 80%. Both mitogenomes had exceptionally low A + T base content and AT skews. We found evidence of pervasive compositional heterogeneity in the dataset and indications that base composition biases cause phylogenetic artefacts. All six mitogenomic analyses produced unique topologies, but all nine analyses produced topologies that rendered Ancyrocephalidae deeply paraphyletic. Mitogenomic data consistently resolved the order Capsalidea as nested within the Dactylogyridea. CONCLUSIONS: The analyses indicate that taxonomic revisions are needed for multiple Polyopisthocotylea lineages, from genera to orders. In combination with previous findings, these results offer conclusive evidence that Ancyrocephalidae is a paraphyletic taxon. The most parsimonious solution to resolve this is to create a catch-all Dactylogyridae sensu lato clade comprising the current Ancyrocephalidae, Ancylodiscoididae, Pseudodactylogyridae and Dactylogyridae families, but the revision needs to be confirmed by another marker with a sufficient resolution.

The complete mitochondrial genomes of Paradiplozoon yarkandense and Paradiplozoon homoion confirm that Diplozoidae evolve at an elevated rate.

BACKGROUND: Diplozoidae are monogenean (Monogenea: Polyopisthocotylea) fish parasites characterised by a unique life history: two larvae permanently fuse into an X-shaped "Siamese" organism. Taxonomy and phylogeny of Diplozoidae and Polyopisthocotylea remain unresolved due to the unavailability of molecular markers with sufficiently high resolution. Mitogenomes may be a suitable candidate, but there are currently only 12 available for the Polyopisthocotylea (three for Diplozoidae). The only available study of diplozoid mitogenomes found unique base composition patterns and elevated evolution rates in comparison with other Monogenean mitogenomes. METHODS: To further explore their evolution and generate molecular data for evolutionary studies, we sequenced the complete mitogenomes of two Diplozoidae species, Paradiplozoon homoion and Paradiplozoon yarkandense, and conducted a number of comparative mitogenomic analyses with other polyopisthocotyleans. RESULTS: We found further evidence that mitogenomes of Diplozoidae evolve at a unique, elevated rate, which was reflected in their exceptionally long branches, large sizes, unique base composition, skews, and very low gene sequence similarity levels between the two newly sequenced species. They also exhibited remarkably large overlaps between some genes. Phylogenetic analysis of Polyopisthocotylea resolved all major taxa as monophyletic, and Mazocraeidea was split into two major clades: (Diplozoidae) + (all four remaining families: Diclidophoridae, Chauhaneidae, Mazocraeidae and Microcotylidae). It also provided further confirmation that the genus Paradiplozoon is paraphyletic and requires a taxonomic revision, so the two species may have to be renamed Indodiplozoon homoion and Diplozoon yarkandense comb. nov. CONCLUSIONS: Although our findings indicate that mitogenomes may be a promising tool for resolving the phylogeny of Polyopisthocotylea, elevated evolutionary rates of Diplozoidae may cause phylogenetic artefacts, so future studies should pay caution to this problem. Furthermore, as the reason for their elevated evolution remains unknown, Diplozoidae are a remarkably interesting lineage for other types of evolutionary mitogenomic studies.

A New Species of Paradiplozoon (Monogenea: Diplozoidae), A Gill Parasite of the Schizothorax Fish (Cyprinidae: Schizothoracinae) from the Yarkand River, Xinjiang, China.

INTRODUCTION: Monogeneans of the genus Paradiplozoon were found on the gills of specimens of five species of schizothoracid caught using fyke nets in the upper stream of the Yarkand River, Xinjiang, China in May-August 2019. METHODS: The preserved parasite were stained with boric acid magenta and hematoxylin, respectively. Morphological observations, line drawings, photomicrographs and measurements were made in Nikon ECLIPSE E200 imaging optical microscope and digitally edited. The molecular analysis included the study of the sequence of the second internal transcribed spacer (ITS 2) of the ribosomal DNA region, calculation and analysis of genetic distance, with phylogenetic reconstructions based on the Bayesian inference and Maximum Likelihood analysis. RESULTS: The natural infection rate of host fish was 10-88%. Morphological analysis indicated that the average length of the new species was 2.125 mm while the width was 0.69 mm. The anterior part was 1.387 mm in length and the average length of the posterior part was 0.545 mm. The vitellaria was well-developed and located in the front of the body. A single ovary (oval shaped) was located at the back end of the reproductive binding area. A testis (irregular mass) was located behind or parallelled to the ovary. The new species can be distinguished from all the recorded Paradiplozoon species in terms of morphological characteristics such as haptor, clamp and central hook morphology, intestine shape and body size. In addition, the second internal transcribed spacer (ITS 2) of the ribosomal DNA region of the diplozoid was compared with that of known diplozoids previously published. It indicated that there were significant differences between the new species and the published diplozoids. CONCLUSION: Both morphological and molecular analysis support that the diplozoid is a new species. Based on the sampling location, the new species was named Paradiplozoon yarkandense n. sp.