eDNA reveals spatial homogenization of fish diversity in a mountain river affected by a reservoir cascade.

One of the main reasons for the decline in global freshwater biodiversity can be attributed to alterations in hydrological conditions resulting from dam construction. However, the majority of current research has focused on single or limited numbers of dams. Here, we carried out a seasonal fish survey, using environmental DNA (eDNA) method, on the Wujiang River mainstream (Tributaries of the Yangtze River, China) to investigate the impact of large-scale cascade hydropower development on changes in fish diversity patterns. eDNA survey revealed that native fish species have decreased in contrast to alien fish. There was also a shift in fish community structure, with declines of the dominant rheophilic fish species, an increase of the small-size fish species, and homogenization of species composition across reservoirs. Additionally, environmental factors, such as temperature, dissolved oxygen and reservoir age, had a significant effect on fish community diversity. This study provides basic information for the evaluation of the impact of cascade developments on fish diversity patterns.

Short daylight photoperiod alleviated alarm substance-stimulated fear response of zebrafish.

Photoperiod has been well-documented to be involved in regulating many activities of animals. However, whether photoperiod takes part in mood control, such as fear response in fish and the underlying mode(s) of action remain unclear. In this study, adult zebrafish males and females (Danio rerio) were exposed to different photoperiods, Blank (12 h light: 12 h dark), Control (12 h light: 12 h dark), Short daylight (SD, 6 h light: 18 h dark) and Long daylight (LD, 18 h light: 6 h dark) for 28 days. After exposure, fear response of the fish was investigated using a novel tank diving test. After alarm substance administration, the onset to higher half, total duration in lower half and duration of freezing in SD-fish were significantly decreased, suggesting that short daylight photoperiod is capable of alleviating fear response in zebrafish. In contrast, comparing with the Control, LD didn't show significant effect on fear response of the fish. Further investigation revealed that SD increased the levels of melatonin (MT), serotonin (5-HT) and dopamine (DA) in the brain while decreased the plasma level of cortisol comparing to the Control. Moreover, the expressions of genes in MT, 5-HT and DA pathways and HPI axis were also altered consistently. Our data indicated that short daylight photoperiod might alleviate fear response of zebrafish probably through interfering with MT/5-HT/DA pathways and HPI axis.

Life Cycle Exposure to Environmentally Relevant Concentrations of Diphenyl Phosphate (DPhP) Inhibits Growth and Energy Metabolism of Zebrafish in a Sex-Specific Manner.

Due to commercial uses and environmental degradation of aryl phosphate esters, diphenyl phosphate (DPhP) is frequently detected in environmental matrices and is thus of growing concern worldwide. However, information on potential adverse effects of chronic exposure to DPhP at environmentally realistic concentrations was lacking. Here, we investigated the effects of life cycle exposure to DPhP on zebrafish at environmentally relevant concentrations of 0.8, 3.9, or 35.6 µg/L and employed a dual-omics approach (metabolomics and transcriptomics) to characterize potential modes of action. Exposure to DPhP at 35.6 µg/L for 120 days resulted in significant reductions in body mass and length of male zebrafish, but did not cause those same effects to females. Predominant toxicological mechanisms, including inhibition of oxidative phosphorylation, down-regulation of fatty acid oxidation, and up-regulation of phosphatidylcholine degradation, were revealed by integrated dual-omics analysis and successfully linked to adverse outcomes. Activity of succinate dehydrogenase and protein content of carnitine O-palmitoyltransferase 1 were significantly decreased in livers of male fish exposed to DPhP, which further confirmed the proposed toxicological mechanisms. This study is the first to demonstrate that chronic, low-level exposure to DPhP can retard growth via inhibiting energy output in male zebrafish.

Phylogenetic perspective on the relationships and evolutionary history of the Acipenseriformes.

The Acipenseriformes, as one of the earliest extant vertebrates, plays an important role in the evolution of fishes and even the whole vertebrates. Here we collected and analyzed all complete mitochondrial genomes of Acipenseriformes species. Phylogenetic analyses demonstrated that the polytomous branch included Acipenseridae and Polyodontidae formed five clades. The Polyodontidae clade and the Scaphirhynchus clade both were monophyletic group, whereas the Acipenser species and the Huso species both were polyphyletic group. The Bayesian divergence times showed that the origin time for Acipenseriformes was at 318.0 Mya, which was similar to the some previous results of 312.1 Mya, 346.9 Mya and 389.7 Mya. The result was in good consistent with the paleontological data available and the split time of the Pacific and Atlantic Oceans from the Jurassic to the Cretaceous (Laurasia splits in North America and Eurasia). The dN/dS ratios showed the evolutionary rates gradually slow down in five major Acipenseriformes clades from the Clade A (the Pacific sturgeons species) to Clade C (the genus Scaphirhynchus), which was related to the process of geographical formation.

Apolipoprotein E Peptide-Guided Disulfide-Cross-Linked Micelles for Targeted Delivery of Sorafenib to Hepatocellular Carcinoma.

Sorafenib (SF) is an FDA-approved molecular-targeted drug for treating hepatocellular carcinoma (HCC). SF, however, suffers from poor water solubility, low bioavailability, dose-limiting side effects, and possible drug resistance. Here, we report on apolipoprotein E peptide-decorated disulfide-cross-linked micellar SF (ApoE-Ms-SF) as a targeted and intelligent formulation for HCC therapy. ApoE-Ms-SF was prepared with a good SF loading of 7.0 wt %, small size (37 nm), high stability, and reduction-triggered drug release from poly(ethylene glycol)-b-poly(ε-caprolactone-co-dithiolane trimethylene carbonate)-mefenamate (PEG-P(CL-DTC)-MA) and ApoE-modified ApoE-PEG-P(CL-DTC) block copolymers. MTT assays in low-density lipoprotein receptors (LDLRs) overexpressing SMMC-7721 human liver cancer cells showed ApoE density-dependent antitumor potency of ApoE-Ms-SF, in which 7.5% ApoE led to the best antitumor effect (IC50: 8.5 vs 23.3 µg/mL for free SF). Confocal studies, flow cytometry, western blot, and apoptotic assays illustrated clearly a more efficient uptake of ApoE-Ms than nontargeted Ms by SMMC-7721 cells as well as lower phosphorylated extracellular signal-regulated kinase protein level and better cell apoptosis caused by ApoE-Ms-SF compared with Ms-SF and free SF. ApoE-Ms-SF revealed a long circulation time (elimination half-life = 6.8 h). DiR-loaded ApoE-Ms showed a significantly higher accumulation in SMMC-7721 tumor than the nontargeted counterpart. The therapeutic outcomes in the orthotopic SMMC-7721 tumor models demonstrated that ApoE-Ms-SF reduced SF-associated side effects and brought about enhanced angiogenesis inhibition and tumor apoptosis compared to free SF and Ms-SF controls, leading to a better treatment of HCC.

Tributyltin enhanced anxiety of adult male zebrafish through elevating cortisol level and disruption in serotonin, dopamine and gamma-aminobutyric acid neurotransmitter pathways.

Tributyltin (TBT), a widely and persistently distributed organontin, has been well documented to disrupt reproduction and behaviors in animals due to its anti-aromatase activity. TBT has been also reported to enhance anxiety in several fish species, whereas the mechanism underlying remains largely unknown. To investigate the disruption of TBT on fish anxiety and the mechanisms possibly involved, adult male zebrafish (Danio rerio) were treated with TBT (100 and 500 ng/L) for 28 days and anxiety behavior was further investigated using a novel tank dive test. Result showed that TBT treatment significantly enhanced the total time of the fish spent in the lower half, delayed the onset time to the higher half of the tank and increased the total duration of freezing of the fish, indicating an enhanced anxiety in TBT-treated fish. Accordingly, TBT sharply elevated the cortisol levels in plasma in a concentration-dependent manner, suggesting that the elevated cortisol level might be involved in the enhanced anxiety. Although the expression of crha was significantly increased and crhbp was significantly decreased in the brain of TBT-treated fish which is consistent to the elevated cortisol level, the expressions of actha and acthb were sharply down-regulated. In contrast, the expressions of genes responsible for the synthesis and action of serotonin (5-HT) (pet1, thp2 and htr1aa), dopamine (DA) (th1, slc6a3, drd2a and drd2b) and gamma-aminobutyric acid (GABA) (gad2 and gabrg2) were all significantly inhibited. The down-regulation of these pivotal genes acting in 5-HT, DA and GABA neurotransmitter systems in response to TBT corresponded well with the TBT-enhanced anxiety in fish. It was thus strongly suggested that these neurotransmitters might be also involved in TBT-enhanced anxiety in adult male zebrafish. The present study extended our understanding of the neurotoxicity of TBT on the anxiety control and behavioral modulation in fish.

Effects of inorganic mercury exposure on histological structure, antioxidant status and immune response of immune organs in yellow catfish (Pelteobagrus fulvidraco).

Mercury (Hg) is well recognized as a highly toxic substance to fish. Nevertheless, little is known about the toxic effects of Hg on immune organs. In this study, we investigated histology, antioxidant status and immune response of the spleen and head kidney in yellow catfish following 6 weeks of exposure to environmentally relevant concentrations of inorganic Hg (2 and 10 µg l-1 Hg2+ ). As expected, Hg accumulation and histological injury in both tissues were observed. Meanwhile, Hg2+ exposure induced oxidative stress, which increased antioxidant enzyme (superoxide dismutase, catalase and glutathione peroxidase) activities, glutathione content, anti-hydroxyl radical capacity and the expression of genes associated with antioxidant (sod1, cat, gpx1, nrf2 and mt) and stress (hsp70) responses in dose- and tissue-specific manners. In the spleen, the mRNA levels of immune-related genes (il-1ß, il-8, tnf-α, il-10, tgf-ß, lys and c3) were upregulated by Hg2+ exposure. However, in the head kidney, upregulation of tnf-α, il-10 and tgf-ß mRNAs and downregulation of il-1ß and lys expressions were observed, while transcriptions of il-8 and c3 were remarkably upregulated only in the 2 µg l-1 group. Overall, our study indicated that Hg2+ exposure could result in Hg accumulation and thereby induced histological impairment, oxidative stress and immunotoxicity in immune organs of yellow catfish, but some enzymes and/or genes involved in antioxidant and immune systems would be activated to resist Hg2+ -induced damage.

Diethylstilbestrol impaired oogenesis of yellow catfish juveniles through disrupting hypothalamic-pituitary-gonadal axis and germ cell development.

Diethylstilbestrol (DES), a non-steroidal estrogen, has been found to cause altered germ cell development and disordered ovarian development in fish females. However, the mechanisms that might be involved are poorly understood. In this study, female juveniles of yellow catfish (Pelteobagrus fulvidraco) (120 days post-hatching) were exposed to two doses (10 and 100 ng l-1 ) of DES for 28 days. After the endpoint of exposure, decreased ovary weight and gonadosomatic index, as well as various ovarian impairments were observed in response to DES. Besides, DES elevated the mRNA levels of vitellogenin 1 (vtg 1) and estrogen receptor 1 (esr 1) in liver and decreased 17ß-estradiol level in plasma. Correspondingly, suppressed mRNA levels of the key genes in the hypothalamic-pituitary-gonadal axis (such as cyp19a1b, gnrh-II, fshß and lhß in brain and fshr, lhr and cyp19a1a in ovary) after DES exposure were also observed. The declined level of plasma 17ß-estradiol and altered gene expressions of genes in the hypothalamic-pituitary-gonadal axis were thus supposed to be closely related to the disrupted oogenesis in DES-treated fish. Analyses further demonstrated that, higher concentration of DES elevated the expression ratio of bax/bcl-2, indicating the enhanced apoptosis occurred in ovary. Moreover, DES upregulated the expressions of genes involved in proliferation (cyclin d1 and pcna), meiotic entry (cyp26a1 and scp3) and meiotic maintenance (dmc1), resulting in arrested oogenesis in catfish. The present study greatly extended our understanding on the mechanisms underlying of reproductive toxicity of DES on fish oogenesis.

Environmentally relevant concentrations of mercury exposure alter thyroid hormone levels and gene expression in the hypothalamic-pituitary-thyroid axis of zebrafish larvae.

Mercury (Hg) is one of the most toxic heavy metals that can cause severe damage to fish. Studies have demonstrated that Hg has a specific affinity for the endocrine system, but little is known about the effects of Hg on thyroid endocrine system in fish. In this study, zebrafish embryos were exposed to environmentally relevant concentrations of 1, 4, and 16 µg/L Hg2+ (added as HgCl2) from 2 h post-fertilization (hpf) to 168 hpf. Thyroid hormone (TH) levels and mRNA expression levels of genes involved in the hypothalamus-pituitary-thyroid (HPT) axis were determined. The results showed that exposure to 16 µg/L Hg2+ increased the whole-body thyroxine (T4) and triiodothyronine (T3) levels. The transcription levels of corticotrophin releasing hormone (crh) and thyroid stimulating hormone (tshß) were up-regulated by Hg2+ exposure. Analysis of the mRNA levels of genes related to thyroid development (hhex, nkx2.1, and pax8) and THs synthesis (nis and tg) revealed that exposure to higher Hg2+ concentrations markedly up-regulated hhex, nkx2.1, nis, and tg expression, while had no significant effect on the transcripts of pax8. For the transcription of two types of deiodinases (deio1 and deio2), deio1 showed no significant changes in all the treatments, whereas deio2 was significantly up-regulated in the 16 µg/L Hg2+ group. In addition, Hg2+ exposure up-regulated thyroid hormone receptor ß (trß) mRNA level, while the transcription of trα was not changed. Overall, our study indicated that environmentally relevant concentrations of Hg2+ exposure could alter TH levels and the transcription of related HPT-axis genes, disturbing the normal processes of TH metabolism.

Diethylstilbestrol arrested spermatogenesis and somatic growth in the juveniles of yellow catfish (Pelteobagrus fulvidraco), a fish with sexual dimorphic growth.

In fish, spermatogenesis and somatic growth are mainly regulated by hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-somatic (HPS) axes, respectively. Xenoestrogens have been reported to impair spermatogenesis in some fishes, and arrest somatic growth in some others, whereas, whether xenoestrogens are capable of disrupting spermatogenesis and somatic growth simultaneously in fish that exhibits sexual dimorphic growth is little known, and the underlying mechanisms remain poorly understood. In this study, male juveniles of yellow catfish (Pelteobagrus fulvidraco), which exhibits a sexual dimorphic growth that favors males, were exposed to diethylstilbestrol (DES) for 28 days. After exposure, DES significantly disrupted the spermatogenesis (decreased gonadal-somatic index (GSI) and germ cell number) and arrested the somatic growth (declined body weight) of the catfish juveniles. Gene expression and plasma steroid analyses demonstrated the suppressed mRNA levels of genes in HPG axis (gnrh-II, fshß, and lhß in the brain and dmrt1, sf1, fshr, cyp17a1, cyp19a1a, and cyp11b2 in the testis) and decreased 17ß-estrodial (E2) and 11-ketotestosterone (11-KT) levels in plasma. Further analysis revealed the arrested germ cell proliferation (cyclin d1), meiosis (dmc1, sycp3), and enhanced apoptosis (decreased bcl-2 and elevated bax/bcl-2 ratio) in the testis. Besides, DES also suppressed the mRNA levels of genes in HPS axis (ghrh, gh, and prl in the brain and ghr, igf1, igf2a, and igf2b in the liver). The suppressed HPG and HPS axes were thus supposed to disturb spermatogenesis and arrest somatic growth in yellow catfish. The present study greatly extended our understanding on the mechanisms underlying the toxicity of DES on spermatogenesis and somatic growth of fish.

Treatment of wastewater containing o-phenylenediamine by ozone in a rotor-stator reactor.

This work employed a novel rotor-stator reactor (RSR) to intensify the degradation process of o-phenylenediamine (o-PDA) by ozone. The effects of different operating parameters including initial pH, temperature, rotation speed, liquid volumetric flow rate and inlet ozone concentration on the removal efficiency of o-PDA were investigated in an attempt to establish the optimum conditions. The removal efficiency was evaluated in terms of degradation ratio and chemical oxygen demand (COD) reduction ratio of the o-PDA wastewater. Results indicate that the removal efficiency decreased with increasing liquid volumetric flow rate but increased with an increase in pH and inlet ozone concentration. Also, the removal efficiency increased up to a certain level with an increase in rotation speed and temperature. Additionally, a comparison experiment was carried out in a stirred tank reactor (STR), and the results show that the degradation and COD reduction ratios reached a maximum of 94.6% and 61.2% in the RSR as compared to 45.3% and 28.6% in the STR, respectively. This work demonstrates that ozone oxidation carried out in RSR may be a promising alternative for pre-treatment of o-PDA wastewater.

Treatment of amoxicillin by O3/Fenton process in a rotating packed bed.

In this study, simulated amoxicillin wastewater was treated by the O3/Fenton process in a rotating packed bed (RPB) and the results were compared with the Fenton process and the O3 followed by Fenton (O3 + Fenton) process. The chemical oxygen demand (COD) removal rate and the ratio of 5-day biological oxygen demand to chemical oxygen demand (BOD5/COD) in the O3/Fenton process were approximately 17% and 26%, respectively, higher than those in the O3 + Fenton process with an initial pH of 3. The COD removal rate of the amoxicillin solution reached maximum at the Fe(II) concentration of 0.6 mM, temperature of 25 °C, rotation speed of 800 rpm and initial pH of 3. The BOD5/COD of the amoxicillin solution increased from 0 to 0.38 after the solution was treated by the O3/Fenton process. Analysis of the intermediates indicated that the pathway of amoxicillin degradation in the O3/Fenton process was similar to that in the O3 + Fenton process. Contrast experiment results showed that amoxicillin degradation was significantly intensified in the RPB.

Bioaccessibility and bioavailability of Pb and Cd in rice is affected by propolis and its extracts and Fe intervention.

Increasing the intake of dietary supplements containing antioxidant components can reduce the oral bioavailability of lead (Pb) and cadmium (Cd) and benefit human health. In this study, the effects of propolis and its extracts (kaempferol (KAE), quercetin (QR), and caffeic acid phenethyl ester (CAPE)) in conjunction with proanthocyanidins (PA) on Pb and Cd bioaccessibility (BAC) and the relative bioavailability (RBA) in brown and polished rice are investigated. The results of in vitro tests showed that propolis and its extracts were effective in reducing Pb BAC in both brown and polished rice. A medium dose of PA had a significant reduction effect on Cd BAC (76 %) and RBA in both brown and polished rice. Based on mouse bioassays, the supplementation of propolis and its extracts significantly (p < 0.05) reduced the Pb-RBA in brown rice, resulting in a decrease in Pb RBA from 25 % in the control group to 16.5-17.6 %. The results showed that the BAC and RBA of Pb in brown rice with dietary supplements decreased significantly, which may be related to the enhanced inhibitory effect of high Fe. It was also found that the Pb RBA was negatively correlated with the Fe content in mice kidneys. This result provided evidence that antioxidants better inhibit the bioavailability of heavy metals, highlighting that propolis and PA may be alternative dietary supplements for intervening in human Pb and Cd exposure.

A mRNA Vaccine for Crimean-Congo Hemorrhagic Fever Virus Expressing Non-Fusion GnGc Using NSm Linker Elicits Unexpected Immune Responses in Mice.

Crimean-Congo hemorrhagic fever (CCHF), caused by Crimean-Congo Hemorrhagic virus (CCHFV), is listed in the World Health Organization's list of priority diseases. The high fatality rate in humans, the widespread distribution of CCHFV, and the lack of approved specific vaccines are the primary concerns regarding this disease. We used microfluidic technology to optimize the mRNA vaccine delivery system and demonstrated that vaccination with nucleoside-modified CCHFV mRNA vaccines encoding GnNSmGc (vLMs), Gn (vLMn), or Gc (vLMc) induced different immune responses. We found that both T-cell and B-cell immune responses induced by vLMc were better than those induced by vLMn. Interestingly, immune responses were found to be lower for vLMs, which employed NSm to link Gn and Gc for non-fusion expression, compared to those for vLMc. In conclusion, our results indicated that NSm could be a factor that leads to decreased specific immune responses in the host and should be avoided in the development of CCHFV vaccine antigens.

Triboelectric Basalt Textiles Efficiently Operating within an Ultrawide Temperature Range.

With the continuous upsurge in demand for wearable energy, nanogenerators are increasingly required to operate under extreme environmental conditions. Even though they are at the cutting edge of technology, nanogenerators have difficulty producing high-quality electrical output at very extreme temperatures. Here, a triboelectric basalt textile (TBT) with an ultrawide operational temperature range (from -196 to 520 °C) is created employing basalt material as the main body. The output power density of the TBT, in contrast to most conventional nanogenerators, would counterintuitively rise by 2.3 times to 740.6 mW m-2 after heating to 100 °C because the high temperature will enhance the material's interface polarization and electronic kinetic energy. The TBT retains ≈55% of its initial electrical output even after heating in the flame of an alcohol lamp (520 °C). Surprisingly, the TBTs output voltage may retain over 85% of its initial value even after submerging in liquid nitrogen. The TBTs exceptional resistance to heat and cold indicates its possible use in high and low latitudes, high altitudes, deserts, and even space settings.

FGF18 encoding circular mRNA-LNP based on glycerolipid engineering of mesenchymal stem cells for efficient amelioration of osteoarthritis.

Mesenchymal stem cells (MSCs) exhibit substantial potential for osteoarthritis (OA) therapy through cartilage regeneration, yet the realization of optimal therapeutic outcomes is hampered by their limited intrinsic reparative capacities. Herein, MSCs are engineered with circular mRNA (cmRNA) encoding fibroblast growth factor 18 (FGF18) encapsulated within lipid nanoparticles (LNP) derived from a glycerolipid to facilitate OA healing. A proprietary biodegradable and ionizable glycerolipid, TG6A, with branched tails and five ester bonds, forms LNP exhibiting above 9-fold and 41-fold higher EGFP protein expression in MSCs than commercial LNP from DLin-MC3-DMA and ALC-0315, respectively. The introduction of FGF18 not only augmented the proliferative capacity of MSCs but also upregulated the expression of chondrogenic genes and glycosaminoglycan (GAG) content. Additionally, FGF18 enhanced the production of proteoglycans and type II collagen in chondrocyte pellet cultures in a three-dimensional culture. In an OA rat model, transplantation with FGF18-engineered MSCs remarkably preserved cartilage integrity and facilitated functional repair of cartilage lesions, as evidenced by thicker cartilage layers, reduced histopathological scores, maintenance of zone structure, and incremental type II collagen and extracellular matrix (ECM) deposition. Taken together, our findings suggest that TG6A-based LNP loading with cmRNA for engineering MSCs present an innovative strategy to overcome the current limitations in OA treatment.

Responses of soil organic carbon compounds to phosphorus addition between tropical monoculture and multispecies forests.

Tropical forests are sensitive to nitrogen (N) and phosphorus (P) availability, and under nutrient application the variation of soil organic carbon (SOC) preserving mechanism remains to be explored. To reveal the forest-specific SOC preservation via biochemical selection in response to nutrient application, we investigated a monoculture (Acacia plantation) and a multispecies forest both with chronic fertilization in subtropical regions, and measured specific fingerprints of plant- and microbial-derived C compounds. In addition, to quantify the effect of P application on SOC content among tropical forests, we conducted a meta-analysis by compiling 125 paired measurements in field experiments from 62 studies. In our field experiment, microbial community composition and activity mediated forest-specific responses of SOC compounds to P addition. The shift of community composition from fungi towards Gram-positive bacteria in the Acacia plantation by P addition led to the consumption of microbial residual C (MRC) as C source; in comparison, P addition increased plant species with less complex lignin substrates and induced microbial acquisition for N sources, thus stimulated the decomposition of both plant- and microbial-derived C. Same with our field experiment, bulk SOC content had neutral response to P addition among tropical forests in the meta-analysis, although divergences could happen among experimental durations and secondary tree species. Close associations among SOC compounds with biotic origins and mineral associated organic C (MAOC) in the multispecies forest suggested contributions of both plant- and microbial-derive C to SOC stability. Regarding that fungal MRC closely associated with MAOC and consisted of soil N pool which tightly coupled to SOC pool, the reduce of fungal MRC by chronic P addition was detrimental to SOC accumulation and stability in tropical forests.

eDNA metabarcoding reveals differences in fish diversity and community structure in heterogeneous habitat areas shaped by cascade hydropower.

Freshwater ecosystems are under great threat from humans, among which habitat heterogeneity is the most obvious, being one of the important reasons for the decline of fish diversity. This phenomenon is particularly prominent in the Wujiang River, where the continuous rapids of the mainstream have been divided into 12 mutually isolated sections by 11 cascade hydropower reservoirs. Based on the fact that conventional survey methods are more harmful to the ecological environment, the efficient and noninvasive environmental DNA metabarcoding (eDNA) approach was used in this study to conduct an aquatic ecological survey of the 12 river sections of the mainstream of the Wujiang River. A total of 2299 operational taxonomic units (OTUs) were obtained, corresponding to 97 species, including four nationally protected fish species and 12 alien species. The results indicate that the fish community structure of the Wujiang River mainstream, which was originally dominated by rheophilic fish species, has been changed. And there are differences in fish species diversity and species composition among the reservoir areas of the mainstream of the Wujiang River. The fish species in the area have gradually declined under the influence of anthropogenic factors such as terraced hydropower and overfishing. The fish populations consequently have demonstrated a tendency to be species miniaturized, and the indigenous fish are severely threatened. In addition, the fish composition monitored by the eDNA approach was found to be close to the fish composition of historical information on the Wujiang River, indicating that eDNA approach may be used as a complementary tool to conventional methods in this basin.

Diversity and spatiotemporal dynamics of fish communities in the Chongqing section of the upper Yangtze River based on eDNA metabarcoding.

Fish diversity plays a critical role in maintaining the balance of water ecosystems, especially in the Chongqing section of the National Nature Reserve for Rare and Endemic Fishes in the upper Yangtze River, which serves as an important habitat for rare and endemic fish, as well as an important channel for the replenishment of fishery resources in the Three Gorges Reservoir. Under a 10-year ban on fishing in the Yangtze River basin, we investigate fish diversity and seasonal variation in the Reserve by using environmental DNA (eDNA) metabarcoding. We found fishes belonging to 85 genera, 24 families, and 8 orders in the Reserve. A comparison of eDNA metabarcoding results with the diversity of a recent fish catch revealed that eDNA metabarcoding not only enables rapid and efficient fish monitoring but also has a high sensitivity. Furthermore, the study demonstrates that eDNA metabarcoding can be used as a tool for monitoring seasonal variations of fish composition in freshwater ecosystems. The alpha and beta diversity analysis both showed compositional differences in the fish community in accordance with seasonal variations. In addition, changes in eDNA relative sequence abundance and the detection of fish species at different sampling sites may reflect shifts in habitat use and distribution. Thus, we provide detailed seasonal data on fish diversity in the Chongqing section of the Reserve. This will contribute to conservation and to the understanding of fish diversity and community dynamics in the Chongqing section of the Reserve.