Background The northeastern part of the Qinghai-Tibet Plateau (QTP) presents a high number of plateau loach species. As one of the three major groups of fishes distributed on the QTP, plateau loach has high ecological value. However, the taxonomy and systematics of these fish are still controversial, and a large number of new species have been reported. The reason for this phenomenon is that the degree of morphological variation is low, the phylogenetic information provided by morphological and anatomical features used for species identification is relatively poor, and many cryptic species are observed. Based on the high-density sampling points from the biodiversity hotspots surveyed, this study aims to evaluate the biodiversity of plateau loach in the northeastern part of the QTP and reveal the hidden diversity by comparing morphological species with molecular operational taxonomic units (MOTUs). Results After careful identification and comparison of the morphology and DNA barcoding of 1630 specimens, 22 species were identified, with 20 considered valid local species and two identified as new species that had not been previously described. Based on the combination of morphological and molecular methods, a total of 24 native species were found, two of which were cryptic species: Triplophysa robusta sp1 and Triplophysa minxianensis sp1. Fourteen of the 24 species form clusters of barcodes that allow them to be reliably identified. The remaining cases involved 10 closely related species, including rapidly differentiated species and species that seemed to have experienced incomplete lineage sorting or showed introgressions. Conclusions The results highlight the need to combine traditional taxonomies with molecular methods to correctly identify species, especially closely related species, such as the plateau loach. This study provides a basis for protecting the biodiversity of plateau loach.

Length‐weight relationships (LWRs) were assessed from four fish species in Hei River in northwest China. All specimens were collected using (fishing1 km along the river and 3 meters along the river bank) and netting (gill nets, nets: 30 × 1.2 m; mesh size: 3 × 3 cm) and shrimp cages (nets: 20.0 × 0.5 × 0.4m; mesh size: 0.5 cm) seasonally from April 2019 to October 2020. The gill nets and shrimp cages were soaked in water in the afternoon and pulled in around 10 a.m. the next day after an overnight stay. These specimens were measured for total length (L, 0.1 cm) and body weight (W, 0.1 g) while the specimens were fresh. The parameters for the LWRs were estimated with the basic statistical analyses. The study provided the new maximum total length for Gymnocypris chilianensis (21.0 cm) and Triplophysa tenuis (17.0 cm).

In this study, we determined the complete mitochondrial genome sequence of Schizothorax davidi. The length of the genome is 16,577 bp, which contains 13 protein coding genes, 22 transfer RNAs, two ribosomal RNAs, and two non-coding regions: control region (D-loop) and origin of light-strand replication (OL). The complete mitochondrial DNA sequence of S. davidi provides useful genetic markers for the studies on molecular systematic, population genetics, and phylogeography.

Background: The northeastern part of the Qinghai-Tibet Plateau (QTP) is one of the areas where the number of species of plateau loach is the largest. As one of the three major groups of fishes distributed on the QTP, plateau loach have very important ecological value. However, their taxonomy and systematics are still controversial, and a large number of new species have been reported. The reason for this phenomenon is that the degree of morphological variation is low, the phylogenetic information provided by morphological and anatomical features used for species identification is relatively poor, and there are many cryptic species. Based on the high-density sampling points from the biodiversity hotspots surveyed, this study aims to evaluate the taxonomic characteristics of the plateau loach by means of morphology, DNA barcoding and multiple species demarcation methods to accurately describe species and allocate taxonomic units to unknown specimens. Results: After careful identification and comparison of the morphology and DNA barcoding of 1,630 specimens, 22 species were identified, 20 of which were considered valid local species and two of which were new species that had not been described. Based on the combination of morphological and molecular methods, a total of 24 native species have been found, two of which are cryptic species: Triplophysa robusta sp1 and Triplophysa minxianensis sp1. Fourteen of the 24 species form clusters of barcodes, which allow them to be reliably identified. The remaining cases involved 10 closely related species, some of which were rapidly differentiated, had a disputed taxonomic status, or showed introgressions.Conclusions: The results highlight the need to combine traditional taxonomies with molecular methods to correctly identify species, especially in closely related species such as the plateau loach. This study provides a basis for protecting the biodiversity of plateau loach.

Background: The northeastern part of the Qinghai-Tibet Plateau (QTP) is one of the areas where the number of species of plateau loach is the largest. As one of the three major groups of fishes distributed on the QTP, plateau loach have very important ecological value. However, their taxonomy and systematics are still controversial, and a large number of new species have been reported. The reason for this phenomenon is that the degree of morphological variation is low, the phylogenetic information provided by morphological and anatomical features used for species identification is relatively poor, and there are many cryptic species. Based on the high-density sampling points from the biodiversity hotspots surveyed, this study aims to evaluate the biodiversity of plateau loach in the northeastern of QTP and reveal the hidden diversity by comparing morphologic species with molecular operational taxonomic units (MOTUs). Results: After careful identification and comparison of the morphology and DNA barcoding of 1,630 specimens, 22 species were identified, 20 of which were considered valid local species and two of which were new species that had not been described. Based on the combination of morphological and molecular methods, a total of 24 native species have been found, two of which are cryptic species: Triplophysa robusta sp1 and Triplophysa minxianensis sp1. Fourteen of the 24 species form clusters of barcodes, which allow them to be reliably identified. The remaining cases involved 10 closely related species, some of which were rapidly differentiated, seemed to have experienced incomplete lineage sorting, or showed introgressions.Conclusions: The results highlight the need to combine traditional taxonomies with molecular methods to correctly identify species, especially in closely related species such as the plateau loach. This study provides a basis for protecting the biodiversity of plateau loach.