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As indicator organisms for water pollution detection, Pseudogasteromyzon species play a vital role in aquatic environment monitoring. We have successfully sequenced the mitogenomes of P. fasciatus jiulongjiangensis and P. myersi and downloaded the mitogenomes of nine other Pseudogastromyzon fish on GenBank to conduct a detailed comparative analysis of their phylogenetic relationships and evolutionary history. The findings revealed a conservation in both gene composition and gene order. Except for the trnS1 gene lacking dihydrouracil arms, the other 21 tRNAs showed the typical clover-leaf secondary structure. According to the ΔRSCU method, we identified the seven most abundant optimal codons: CUA, GUA, CCA, CAA, GAA, AGC, and GGC. The construction of maximum parsimony, maximum likelihood, and Bayes trees yielded congruent topologies, and the 11 Pseudogastromyzon species were clustered into two major clusters. Among them, one of which was composed of P. fangi, P. changtingensis changtingensis, and P. changtingensis tungpeiensis, while the remaining eight species formed another cluster, further subdivided into five smaller clusters. Distinct clusters formed between P. fasciatus jiulongjiangensis and P. meihuashanensis, P. cheni and P. peristictus, and P. laticeps and P. lianjiangensis, and the remaining two species were clustered separately, thereby enhancing our understanding of them. Furthermore, our analysis results of divergence times revealed that these 11 Pseudogasteromyzon species underwent rapid differentiation in the Pleistocene epochs. Overall, our study sheds light on the phylogenetic relationship and evolutionary history of Pseudogasteromyzon species, providing a necessary knowledge foundation for further understanding the intricacies of an ecosystem health assessment. Full article

In order to determine the relationship between stream habitat and fish assemblages, an investigation of fish assemblages and environmental variables in different habitat types was carried out in the headwater stream section of Lijiang River, China, from September to November 2016. In total, 2968 individuals belonging to 4 orders, 11 families, 26 genera and 37 species were collected. Cypriniformes emerged as the most species-rich order, accounting for 62.2% of the total species. The dominant species were Pseudogastromyzon fangi, Zacco platypus, Acrossocheilus parallens and Erromyzon sinensis. Non-metric multidimensional scaling (NMDS) and permutational multivariate analysis of variance (PERMANOVA) revealed that fish assemblages were not affected by habitat type. However, one-way ANOVA results showed that species richness, fish abundance, fish density and Shannon index were significantly affected by habitat type. Redundancy analysis (RDA) further revealed that altitude, velocity, conductivity, turbidity, depth and wetted width had significant relationships within fish assemblages, whereas water temperature, dissolved oxygen and substrate size were less important in this study, and different fish species preferred different environmental variables potentially due to differences in species’ ecological requirements. Although habitat type did not affect overall fish assemblages, habitat heterogeneity played an important role in fish diversity. Hence, maintaining diverse stream habitats or restoring them are of key importance for fish diversity conservation and sustainability management of rivers. Full article