Seasonal water-level fluctuations may lead to changes in river nutrients, which causes corresponding changes in the trophic structure of an aquatic food web, and finally affects the whole ecosystem. In this study, we focused on the Ganjing River, a tributary of the Yangtze River, China. Common organisms were sampled and measured for carbon and nitrogen stable isotopes in the wet and dry seasons, respectively, and the relative contributions of different food sources were combined to construct the food web, so as to realize the influence of water-level fluctuation on aquatic food web. Our results showed that basal food sources for fish consumers were endogenous carbon sources such as POM, zooplankton and zoobenthos in the dry season, while high water level exposed fish to more diverse and abundant food sources, and the contribution proportions of exogenous carbon sources (e.g., terrestrial detritus) to consumers increased in the wet season. In parallel, the abundance and species diversity of fish were higher than those in the dry season. Most fish species had relatively higher trophic levels in the dry season compared to the wet season, because the increase in fish densities led to an increase in piscivores fish. The food web was composed of planktonic and benthic food chains in the dry season. During the wet season, the planktonic food chain was dominant, followed by the herbivorous food chain, and the benthic food chain was relatively less important. Therefore, water-level fluctuation may alter the trophic linkages within fish communities, which contributed to a more complex and interconnected food web. Moreover, as we expect, the stable isotope analysis food web was broadly in line with the gut content analysis food web.

Lepturichthys fimbriata is an endemic and an important commercial fish which distributes in the upper stream of the Yangtze River. In this study, the complete mitogenome sequence of L. fimbriata has been first sequenced by DNA sequencing based on the PCR fragments. The mitogenome, consisting of 16,567 base pairs (bp), includes 13 protein coding genes, 22 transfer RNAs, 2 ribosomal RNA genes and a non-coding control region (CR). The overall base composition of L. fimbriata is 30.4% A, 28.7% C, 16.5% G, and 24.4% T, with a relatively a slight AT bias of 54.7%. CR of 903 bp length is located between tRNA^Pro and tRNA^Phe. The complete mitochondrial genome sequence would be useful for further studies on conservation genetics and resource management in L. fimbriata.

The Bighead carp (Hypophthalmichthys nobilis), a primary freshwater aquaculture species in China, faces challenges due to over-exploitation and environmental changes. We leveraged RAD-seq to perform a comprehensive population genetic analysis on 14 H. nobilis populations sampled from the Yangtze River (13 populations) and the Marseilles Reach of the Illinois River (one population). Analysis of genetic diversity showed that different parameters demonstrated varied inferences, and notably, Zhongxian (ZX2), Wanhzou (WZ2), Yangzhou hatchery (YZYZ), Yangzhou (YZ), and Taihu (TH) populations showed apparent heterozygote deficiency. Linkage disequilibrium (LD) analysis exhibited a trend of higher linkage disequilibrium in populations from the upper reaches of the Yangtze River, followed by those from the middle reaches and then those from the lower reaches. Additionally, the reconstructed polygenetic tree and PCA plot clustered all populations into 2 major subgroups, while the results of structure analysis indicated 4 ancestors. The pairwise F_ST values ranged from 0 to 0.5530. Among these, high F_ST values (0.1931–0.5530) were only observed between populations WZ2, YZ, YZYZ, and the remaining 11 populations. Furthermore, genetic bottlenecks were observed in all populations 20–30 thousand years ago. Overall, the research offers insights essential for genetic management practices for sustainable aquaculture and biodiversity conservation of bighead carp.

In this study, the complete mitochondrial DNA genome sequence of Sinibrama taeniatus was first determined by DNA sequencing based on the PCR fragments. The complete mitochondrial DNA (mtDNA) genome sequence of S. taeniatus was a circular molecule of 16,623 bp in length. It consisted of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region (D-loop). The gene nucleotide composition of S. taeniatus was 31.3% A, 26.8% C, 16.1% G, and 25.8% T, with a relatively high A + T content (57.1%). The results could provide useful data for studying genetic diversity and phylogenetics in S. taeniatus and related species.

Human activities have altered rivers worldwide, but how their combined effects shape fish assemblages remains unclear. We therefore surveyed fish and habitats seasonally along the middle and lower reaches of the Han River, China, during 2022, specifically in June–August (wet season) and October–November (dry season). This study analyzed the spatial distribution pattern of fish diversity, explored the effects of natural factors (e.g., hydrology, water quality) and human stressors (e.g., dam, land use) on the spatial pattern of fish diversity, and identified the key driving factors. Cluster analysis and Non-metric Multidimensional Scaling (NMDS) showed that the fish communities could be divided into three groups: the Danjiangkou reservoir area (DRA), the middle reaches (MR), and the lower reaches (LR). For α-diversity, the LR had the highest value, followed by the DRA, with the MR being the lowest. For β-diversity, the MR had the highest value, followed by the LR, with the DRA being the lowest. Random Forest model showed that fish diversity was mainly affected by natural factors; among these factors, the key drivers of α-diversity were hydrological factors such as the water level (3.56–5.97%) and river width (4.53–4.69%), while for β-diversity, the key drivers were water quality factors, including the dissolved oxygen (10.08–12.36%), total nitrogen (6.49–9.31%), and chlorophyll a (8.26–8.40%). Structural Equation Modeling further revealed that natural factors affected β-diversity mainly through direct pathways, while human stressors affected β-diversity mainly through indirect pathways. The results revealed the differential roles of natural factors and human stressors in driving the patterns of fish α-diversity and β-diversity in human-disturbed rivers, which will provide a scientific basis for the conservation of fish diversity in the Han River.