Background: The distribution of the Chinese Glyptosternoid catfish is limited to the rivers of the Tibetan Plateau and peripheral regions, especially the drainage areas of southeastern Tibet. Therefore, Glyptosternoid fishes are ideal for reconstructing the geological history of the southeastern Tibet drainage patterns and mitochondrial genetic adaptions to high elevations. Results: Our phylogenetic results support the monophyly of the Sisoridae and the Glyptosternoid fishes. The reconstructed ancestral geographical distribution suggests that the ancestral Glyptosternoids was widely distributed throughout the Brahmaputra drainage in the eastern Himalayas and Tibetan area during the Late Miocene (c. 5.5 Ma). We found that the Glyptosternoid fishes lineage had a higher ratio of nonsynonymous to synonymous substitutions than those found in non-Glyptosternoids. In addition, ω_pss was estimated to be 10.73, which is significantly higher than 1 (p-value 0.0002), in COX1, which indicates positive selection in the common ancestral branch of Glyptosternoid fishes in China. We also found other signatures of positive selection in the branch of specialized species. These results imply mitochondrial genetic adaptation to high elevations in the Glyptosternoids. Conclusions: We reconstructed a possible scenario for the southeastern Tibetan drainage patterns based on the adaptive geographical distribution of the Chinese Glyptosternoids in this drainage. The Glyptosternoids may have experienced accelerated evolutionary rates in mitochondrial genes that were driven by positive selection to better adapt to the high-elevation environment of the Tibetan Plateau.

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.

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.

Sturisomatichthys panamense(Loricariidae, armored catfishes) is widespread throughout Central and South America from Pacific slope rivers of Panama to Caribbean slope rivers of Colombia. Due to the...

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.