Xiuhui Ma

The seasonal monitoring of fish communities was conducted in the Xijiang River Basin of Guizhou Province using environmental DNA (eDNA) metabarcoding technology. A total of 97 fish species were identified during the 2023 survey, representing a detection rate of 61.94% compared to historical records. The findings demonstrated the following: (1) Fish communities exhibited significant spatiotemporal heterogeneity, with species diversity and composition varying seasonally and spatially; (2) human activities, such as reservoir construction, have led to the potential trend toward miniaturization of fish populations and pose a severe threat to the survival of indigenous species; (3) water NH₃‐N, altitude, and pH emerged as the key environmental factors influencing community structure. This research elucidated the dynamic characteristics of riverine fish communities in karst mountainous regions and provided a scientific foundation for the adaptive management of river basin ecosystems. Furthermore, this study represents the validation of eDNA technology's monitoring efficiency in karst areas characterized by complex geographical environments, thereby confirming its application value in assessing biodiversity in mountainous aquatic systems.

Dam construction alters river hydrology, influencing the temporal and spatial heterogeneity of fish communities. This study utilized environmental DNA (eDNA) sequencing to analyze seasonal variations in fish communities in the Duliu River, Guizhou Province, and to assess the impact of hydrological regulation on biodiversity. High-throughput sequencing revealed that sequence reads were significantly higher in the dry season than in the wet season (P < 0.05), while operational taxonomic unit (OTU) richness was greater in the wet season. A total of 69 fish species (6 orders, 18 families) were detected in the dry season, with only 23 species matching historical records. eDNA sequencing identified an additional 46 species, primarily from the order Cypriniformes. In the wet season, 82 species (7 orders, 17 families) were recorded, including 44 species not found in historical data. Cypriniformes dominated in both seasons, comprising 94% of the community in the dry season and 82% in the wet season. Spatial heterogeneity analysis using principal coordinates analysis (PCoA) indicated significant differences among river sections (PC1 = 65.2% in the dry season; 83.65% in the wet season). Beta diversity analysis (NMDS) confirmed significant temporal and spatial variation in fish communities (P < 0.05). This study highlights the ecological impact of dam construction on fish communities and underscores the need for conservation strategies to protect biodiversity in regulated mountain rivers.

The Nujiang River is rich in aquatic biodiversity, especially endemic fish. However, long-term human interference, such as cascade hydropower construction, has significantly changed aquatic habitats and threatened populations’ number and genetic diversity. This study used two mitochondrial gene markers, cyt b, and COI, combined with microsatellite molecular markers developed based on transcriptome data, which were used to study the genetic structure and genetic diversity of Placocheilus cryptonemus in Nu River. The cyt b gene showed that the haplotype mismatch distribution map of the P. cryptonemus population showed a unimodal distribution, indicating that the population expansion may occur during the evolutionary process. Microsatellite analysis showed high information content with high genetic diversity, the whole population was moderately genetically differentiated. There are certain differences in various molecular markers, and the results obtained are not completely consistent, but the overall results show that the level of genetic diversity among the populations of P. cryptonemus is moderate, and the genetic differentiation was not obviously, but the genetic differentiation of the mainstream population in different river basins was obviously. It may be related to different geographical and climatic differences, as well as the species’ own habitat habits.

The construction of a reservoir dam alters the environment within its basin, including composition of the fish community, fish biodiversity, and the river ecosystem itself. This study was conducted in the Sanbanxi Reservoir and used eDNA metabarcoding technology comprising eDNA capture and extraction, PCR amplification, sequencing and database comparison analysis, and other environmental DNA metabarcoding standardized analysis processes to characterize the composition and diversity of fish communities and assess their current status. A total of 48 species of fish were detected. Previously, 68 species of fish were screened and identified in this reservoir based on the reports of Dai and Gu. The results for fish community composition showed that species of the order Cypriniformes are still the most dominant in the Reservoir with 38 species of cyprinids, accounting for 90.81% of all OTUs. Carp were no longer the dominant species, and Spinibarbus denticulatus, Homalopteridae, Cobitidae, and Sisoridae were not detected, with the exception of Misgurnus anguillicaudatus (Cobitidae). These families have the common characteristic of being adapted to survive in fast-water, sandstone substrate habitats. The results also show that two of the sampling sites, sbx03 and sbx10, significantly differed from other sampling sites due to their geographical environment. The impact of the construction of reservoirs on freshwater fish communities is extreme, since the transformation from a lotic to a lentic habitat contributes to habitat destruction and constrains fish in movement. The change in the aquatic environment before and after the storage of water in the Sanbanxi Reservoir has reduced the number of fish species found in the reservoir, and species characteristically found in fast moving, rapids habitats are virtually absent. The profound change in the aquatic environment from that of a lotic to a lentic habitat leads to changes in the composition of fish populations in the reservoir and to a certain extent a reduction in the ecological stability and species diversity within the reservoir. Therefore, the protection of fish diversity in the reservoir is of great significance to the stability of the ecosystem.

The complete mitochondrial DNA genome of Pseudopimelodus schultzi was first was determined in this study. The entire length of mitochondrial genome consists of 13 protein-codinggenes (PCG), 2 ribosomal RNA genes (rRNA), and 22 transfer RNA (tRNA) genes and control region. The nucleotide composition was made up of 32.2% A, 25.9% T, 26.7% C, and 15.2% G, respectively, indicating an A + T (58.1%)-rich feature. With the exception of 8 tRNA genes and NADH6, mitochondrial genes are encoded on the heavy strand, which was similar to that in other vertebrates. The results showed that the species of Pseudopimelodidae were gathered in the same branch. The phylogenies indicate monophyly of the genus Batrochoglanis, Batrochoglanis and Microglanis, respectively.

The complete mitochondrial DNA genome of Sorubim lima was first reported by next-generation sequencing method. The entire length of mitochondrial genome is 16,539 bp and the nucleotide composition was made up of 32.1% A, 24.9% T, 28.0% C, and 15.0% G, indicating an A + T (57.0%)-rich feature. With the exception of 8 tRNA genes and NADH6, mitochondrial genes are encoded on the heavy strand, which was similar to that in other vertebrates. The results showed that the species of Pimelodidae were gathered in the same branch. The phylogenies indicate monophyly of the genus Pseudoplatystoma, Pimelodus and Sorubim.

Organisms living at high altitudes face low oxygen and temperature conditions; thus, the genetic mechanisms underlying the adaptations in these organisms merit investigation. The glyptosternoid fish, Creteuchiloglanis macropterus mainly inhabits regions with gradual increases in altitudes along the Nujiang River and might serve as an appropriate evolutionary model for detecting adaptation processes in environments with altitude changes. We constructed eleven RNA-sequencing (RNA-seq) libraries of C. macropterus collected from five locations at different altitudes to identify the genetic signatures of high-altitude adaptation. The comparative genomic analysis indicated that C. macropterus has an accelerated evolutionary rate compared with that of fishes in the lowland, and fishes at higher altitudes might evolve faster. Functional enrichment analysis of the fast-evolving and positively selected genes, differentially expressed genes and highly expressed genes, showed that these genes were involved in many functions related to energy metabolism and hypoxia. Our study provides evidence of high-altitude adaptation in C. macropterus, and the detected adaptive genes might be a resource for future investigations of adaptations to high-altitude environments in other fishes.