To assess the applicability of environmental DNA (eDNA) technology in monitoring fish diversity in Dongting Lake, located in Hunan Province within the Yangtze River Basin, China, this study combined eDNA metabarcoding with traditional fishing gear to describe the diversity characteristics of the fish community in its habitat. Water samples were collected from 20 representative sites for eDNA analysis, followed by filtration, DNA extraction, and high-throughput sequencing targeting the 12S rDNA region. Concurrently, traditional fishing gear using gill nets and fish traps was conducted at the same locations. The results revealed 82 fish species detected by both methods combined, with eDNA alone identifying 21 species (including rare species encompassing Saurogobio gracilicaudatus and Glyptothorax sinense), while traditional fishing gear detected 27 species. Among the 82 fish species, a total of thirty-four species of fish could be observed in catches from both methods. In terms of α-diversity, eDNA showed higher Chao1, species richness, and ACE indices compared to traditional fishing gear, but lower Shannon and Simpson indices. eDNA was more sensitive to species richness, while traditional fishing gear was better at characterizing community evenness and diversity. β-Diversity analysis showed higher spatial similarity in the fish community structure detected by eDNA, while traditional fishing gear revealed significant differences between the upstream and downstream areas. In summary, eDNA technology has the advantages of non-invasiveness, high sensitivity and broad coverage, effectively serving as a valuable supplementary tool of traditional fishing gear, particularly in monitoring rare species. However, further improvements are needed in terms of species abundance quantification and database dependency. The combination of these two methods provides a more comprehensive scientific basis for fish resource conservation in Dongting Lake.

This study investigated heavy metal bioaccumulation, pollution sources, and human health risks in the Wujiang and Zhenjiang rivers, the major headwaters of the Beijiang River in southern China. Concentrations of 11 heavy metals (Fe, Mn, Ba, Zn, As, Cu, Ni, Cr, Co, Cd, Pb) in surface water, sediments, and the soft tissues of four bivalve species (Corbicula fluminea, Limnoperna fortunei, Unio douglasiae, and Anodonta woodiana) were determined. Results showed that surface water remained below pollution thresholds, whereas sediments in the Wujiang River exhibited moderate-to-heavy Cd, As, Pb, and Zn contamination linked to historical Pb-Zn mining. Among the two better-represented species, C. fluminea showed relatively high As and Zn concentrations, whereas L. fortunei showed relatively high Cu accumulation. Data for U. douglasiae and A. woodiana were treated as preliminary observations because of their limited sample sizes. Biota-sediment accumulation factor (BSAF) values indicated that Mn, Cu, Cd, Zn, Ni, and Cr were actively accumulated beyond sediment concentrations, whereas As and Pb showed limited sediment-to-biota transfer. Multivariate analysis of the two better-represented species indicated species-related differences in tissue metal profiles, with patterns consistent with both natural geogenic inputs and historical Pb-Zn mining activities. All four species posed potential non-carcinogenic health risks to consumers, with As and Mn as the dominant risk contributors. These findings underscore the necessity of multi-species biomonitoring and consumption advisories in mining-impacted watersheds.

Pyrethroids serve as a significant method for managing and preventing parasitic diseases in fish. Among these, deltamethrin (DEL) is used extensively in aquatic environments. Our previous work has been confirmed that DEL exposure can induce oxidative stress and immunosuppression on the gill mucosal barrier of crucian carp (Carassius auratus). However, it is not clear whether DEL affects the susceptibility of farmed fish to bacterial infection. In this study, fish was pre-exposed to different DEL concentration (0, 0.3 and 0.6 μg L^-1) and then challenged by immersion with Aeromonas hydrophila (1.0 × 10ˆ8 CFU mL^-1). After immersion challenge, fish pre-exposed to DEL developed prominent lipopolysaccharides level in gill and serum and had a significantly lower survival rate compared to the control group. In DEL pre-exposure fish after immersion, the gill apoptosis levels were significantly higher and disrupted the tight junction barrier by downregulating the zo1 and claudin12. Furthermore, fish pre-exposed to DEL exhibited increased activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and malonaldehyde (MDA) levels in the early stage after immersion but experiencing decreased activities of glutathione peroxidase (GPx) and lysozyme (LZM) in the later stage after immersion. And this process was regulated by the NRF2 pathway. Additionally, fish pre-exposed to DEL after immersion had significantly lower mRNA levels of immune-related genes tlr4, myd88, tnfα, and il-1β. Overall, these findings indicate that DEL damaged the gill barrier, weakened the immune response, raised LPS levels, and heightened vulnerability to A. hydrophila infection in crucian carp, resulting in mortality. Thus, this work will help social groups and aquaculture workers to understand the potential risk of DEL exposure for bacterial secondary infection in cultured fish.

Bismuth oxychloride (BiOCl) has garnered significant research interest owing to its non-toxicity, affordability, and distinct layered structure. Although BiOCl possesses promising photocatalytic potential, its large band gap and rapid photocarrier recombination restrict its practical use. In this work, a natural tourmaline mineral was effectively integrated with BiOCl to form a composite (TBO). Comprehensive characterization and photocatalytic assessments revealed that the intrinsic electric field of tourmaline notably strengthened both the adsorption capacity and the light-driven catalytic efficiency of BiOCl. Under visible-light irradiation, ofloxacin (OFX, 10 ppm) was eliminated by approximately 98% within 60 min. The apparent reaction rate constant (k) of TBO was 0.0407 min⁻¹, which was approximately 184.8 and 2.26 times those of tourmaline alone and pristine BiOCl, respectively. Furthermore, both the visible-light absorption and the separation efficiency of photogenerated electron–hole pairs were significantly enhanced. After evaluating its behavior under various simulated natural environmental conditions, TBO displayed strong potential for practical application. Reactive species trapping and analysis identified singlet oxygen (¹O₂) and superoxide radicals (·O₂⁻) as the primary active species in photocatalysis. Moreover, the degradation route of ofloxacin and the toxicity of its intermediates were systematically examined. These findings offer meaningful guidance for improving photocatalytic materials by utilizing naturally occurring minerals.

Parasitic infections pose a significant threat to the wild population of Southern catfish (Silurus meridionalis) in Dongting Lake, yet the specific pathogen identity and epidemiological drivers remain unclear. This study combined morphological assessment, 28S rDNA molecular identification, and Generalized Linear Models (GLM) to elucidate the infection dynamics and pathogenicity of trematodes. Molecular analysis confirmed the pathogen as Isoparorchis eurytremus. GLM analysis revealed that apparent spatiotemporal variations in infection were actually sampling bias in fish host size structure; the total length was identified as the decisive predictor of infection risk. The infection probability followed a sigmoid growth pattern with a median infection length (L₅₀) of 70.4 cm, a phenomenon attributed to the host’s ontogenetic diet shift from insectivory to obligate piscivory. Anatomical observations indicated that the infection induced systemic pathology; beyond severe fibrosis and mechanical damage to the swim bladder, varying degrees of parenchymal lesions were evident in the liver, spleen, and kidney. These findings indicate that I. eurytremus infection in S. meridionalis is a size-dependent, accumulative process maintaining a homogenous high pressure across the lake ecosystem, necessitating a shift in perspective from localized lesions to systemic disease management.