摘要: Nocardia seriolae alters macrophages to a “foamy” phenotype characterized by the accumulation of lipid droplets during infection to create a habitat that is ideally suited to its requirements. However, little is known about how exactly it does this. We extracted and identified specific lipids from N. seriolae, mycolic acids (NsMA), and confirmed they induced foam cells for granuloma formation in a snakehead (Channa argus) model. RNA-sequencing revealed that NsMA-induced foam cells were associated with Coronin-1A, which was further supported by Coronin-1A binding to NsMA as well as to the wild-type strain ZJ0503 rather than the NsMA-deficient strain ΔfadD32. An in vitro assay revealed that the NsMA-induced Coronin-1A was responsible for inhibiting autophagy, whereas the inhibitory effect of autophagy was reversed in macrophages before receiving an anti-Coronin-1A antibody or mTOR inducer treatment. Meanwhile, the same results were also found by RNA interfering in vivo: silencing coronin-1A activated autophagy in NsMA-challenged snakehead, thereby alleviating the symptoms of granuloma formation with foam cell populations. Taken together, these results demonstrate that NsMA depends on the host's Coronin-1A to inhibit autophagy through the mTOR pathway, and thereby promotes cell foam for granuloma formation in N. seriolae-infected fish.

摘要: Nano-additives can improve the absorption and utilization of feed nutrients. In this study, we reported the effects of supplementary nano iron (0, 30, 60, 120, 240 and 480 ​mg/kg) on intestinal tract function of largemouth bass juveniles. Firstly, 60 ​mg/kg of supplementary nano iron improved specific growth rates of largemouth bass, and significantly increased the height and width of intestinal villi and intestinal absorption area. Secondly, supplementation of low concentrations of nano iron through intraperitoneal injection significantly increased the activity of intestinal antioxidant enzymes catalase and total superoxide dismutase (CAT and T-SOD), enhanced the expression of antioxidant-related genes (sod1, nrf-2) and proteins (CAT; P ​< ​0.05), and decreased malondialdehyde (MDA) content, resulting in higher survival rates of Nocardia seriolae. Supplementation of 480 ​mg/kg compromised the immune and antioxidant capacity of juvenile largemouth bass, as evident by the increased expression of inflammatory and apoptotic genes, significant reduction in the expression of intestinal tight junction genes (zo-1, claudin1, claudin7; P ​< ​0.05), impairment of intestinal physical barriers, and exacerbation of oxidative stress levels. Through quadratic regression analysis, the optimal dietary supplementation level of nano iron for juvenile largemouth bass was determined to be approximately 80 ​mg/kg. In conclusion, moderate supplementation of nano iron appears to enhance the intestinal physical barrier, antioxidant capacity, and immune function of juvenile largemouth bass.

摘要: Grass carp (Ctenopharyngodon idella), a cornerstone of global freshwater aquaculture, face severe threats from grass carp reovirus II (GCRV-II), which causes massive mortality and economic losses. While vaccines targeting GCRV-II antigenic proteins have shown promise, their efficacy is limited by suboptimal antigen presentation. This study focused on enhancing immune responses by leveraging antigen-presenting cell (APC) receptors, particularly TLR22a, to improve antigen recognition and uptake. Utilizing the immunodominant vp4-3 epitope of GCRV-II, GFP-fused recombinant proteins (N-vp4-3 and C-vp4-3) were constructed via a eukaryotic expression system. Immunization trials in grass carp revealed that N-vp4-3 significantly upregulated APC receptor genes (TLR22a and CR1) and immune-related markers (MHC-II and CD80/86) in spleens and kidneys. Co-immunoprecipitation and confocal microscopy confirmed the direct interaction between N-vp4-3 and TLR22a. Computational modeling and single amino acid random mutagenesis identified the ^V96^W mutation in N-vp4-3 as optimal for TLR22a binding, yielding enhanced stability and interaction energy. Immunization with the N-vp4-3-^V96^W mutant induced a 616-fold increase in TLR22a expression, significantly elevated serum IgM titers (3.61-fold), and enhanced the survival against GCRV-II challenge by 48.78 ​%, surpassing the unmodified antigen. Conversely, the destabilizing N-vp4-3-^A59^P mutation showed negligible efficacy. These findings highlight the critical role of TLR22a in APC-mediated immunity and demonstrate structure-guided antigen design as a potent strategy for vaccine optimization. This study provides critical insights into APC receptor activation mechanisms and establishes a framework for developing high-efficacy vaccines against GCRV-II and related pathogens.

摘要: Freshwater ecosystems are increasingly threatened by different human stressors, thereby jeopardizing aquatic biota. Macroinvertebrates are one of the most common bioindicators used worldwide to assess the biological condition of ecosystems. In this study, we systematically reviewed the literature on the use of macroinvertebrates as biological indicators in freshwater ecosystems in Brazil, highlighting the impacts of human activities. Following Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, we analyzed 175 articles published up to June 2023 extracted from the Scopus and Web of Science databases. We summarized information on temporal and spatial trends, type of aquatic environment, biological metrics used, taxonomic levels, and sources of anthropogenic stressors. We found an increase in the number of studies over time and a biased geographical distribution, in which the Paraná hydrographic region was the most studied by far. Lotic systems were the most common type of environment, and most studies identified individuals at the family level and used metrics such as taxonomic richness, diversity, and abundance in contrast to functional, morphological, or physiological metrics. The main reported stressors were water quality and habitat changes, often associated with urbanization and agriculture. To support effective monitoring and conservation policies in a megadiverse country, it is important to improve knowledge of human stressors on freshwater communities, and the findings of this study are crucial for understanding how human activities have impacted freshwater communities in tropical ecosystems.

摘要: Fish osmoregulation was characterized by modifications in both the structure and functionality of numerous osmoregulatory cells and organs. Single-cell resolution investigations are imperative for comprehending the cellular processes involved in salinity-induced stress in fish. In this study, a cell atlas of the kidney of Genetically Improved Farmed Tilapia (GIFT) exposed to 27 ​ppt high-salinity stress for one month was established using scRNA-seq. We first identified 16 principal cell clusters, including podocytes (PODs), vascular endothelial cells (VasEndo), T cells, parietal epithelial cells (PECs), renal interstitial cells (RICs), vascular smooth muscle cells (SMCs), distal early tubule (DE), proximal convoluted tubule (PCT), B cells, hematopoietic stem/progenitor cells (HSPCs), macrophages/dendritic cells (MΦ/DCs), renal progenitor cells (RPCs), juxtaglomerular apparatus (JGA), proximal straight tubule (PST), and multiciliated cells (MCCs). A notable augmentation in the gene expression and proportions of PECs was observed, underscoring their pivotal function in the adaptive response of the kidney to high salinity stress. Analysis of RNA velocity unveiled a transitional connection between PECs and PODs, suggesting that PECs might act as precursor cells for PODs. Particularly, mature podocytes (MP) displayed resilience in high-salinity conditions, with kirrel1b, situated at the QTL region LG18: 26,733,536–26,809,639, pinpointed as a distinguishing novel gene marker for MP and a potential candidate gene for salinity endurance. Interestingly, the high-salinity levels substantially suppressed the expression of genes linked to lipid metabolism, such as plin2, srebf2, and dgat1, in renal tubular epithelial cells (PCT, PST, and DE), indicating a decline in lipid droplet formation and lipid synthesis. These discoveries provided valuable perspectives into the cellular and molecular mechanisms involved in salinity adaptation in tilapia.

摘要: Light intensity directly affects phytoplankton and can alter the toxicity of phytotoxic pollutants present in natural water bodies. Light fluctuation in aquatic ecosystems often occurs as a function of water turbidity, water movement, cloud cover, and seasonality. Atrazine and simazine are commonly used herbicides that inhibit photosynthesis, posing significant risks to aquatic primary producers, and may be found simultaneously in aquatic ecosystems. The interactions between light and herbicide mixtures on phytoplankton growth and physiological state are poorly understood. Therefore, we addressed the toxicity of the herbicides, atrazine and simazine (individually and mixed), on the growth and photosynthetic activity of three freshwater phytoplankton under three light intensities. We found that the toxic effects of single and mixed herbicides are species-specific and significantly modulated by light intensity, with synergistic effects observed for herbicide mixtures under high light conditions. Atrazine and simazine (individually and mixed) toxicities on photosynthesis were greater for the three species grown under low light than under very low light. However, high-light adapted strains of M. aeruginosa were less sensitive to single and mixed herbicides than those adapted to low- and very low-light conditions. Under low- and high-light conditions, the photoprotective ability was extremely sensitive to the inhibitory effects of atrazine and simazine, individually and when mixed. Understanding these interactions is important because microalgae form the base of aquatic food webs and their impairment can have cascading effects on ecosystems. These findings underscore the importance of considering multiple environmental stressors in assessing the ecological risks of herbicides, highlighting potential impacts on aquatic primary productivity.

摘要: Chemical pollution is a widespread stressor for wild organisms, but its effects on molecular damage and aging are still poorly understood. Telomere attrition has been used as an integrative biomarker of aging and stress exposure in endotherms. However, the effects of organic pollution on telomere length remain unclear, especially in ectotherms such as fish. We compared telomere length in fish gills across different populations of a short-lived invasive species, the mosquitofish (Gambusia holbrooki), exposed to organic pollution, or salinity. We expected lower telomere length in fish from more polluted and/or saline habitats due to increased oxidative stress. Contrary to our predictions, telomere length was unchanged in agricultural and port habitats and was higher in populations exposed to increased salinity and industrial pollution. A significant change in oxidative stress status in the liver was observed in response to increased salinity but no clear response was evident regarding pollution. Although the underlying mechanisms remain to be explored, this study suggests protective processes limiting telomere attrition or selective processes favoring individuals with longer telomeres. We also encourage further empirical approaches to study telomere attrition in aquatic ectotherms, particularly in fish exposed to multiple environmental stressors.

摘要: The Paraopeba River, one of the largest tributaries of the São Francisco River basin, extends approximately 500 ​km and drains a densely populated region in Minas Gerais, Brazil. The aquatic ecosystems of the Paraopeba River have been subjected to various anthropogenic pressures, including habitat degradation, pollution from agrochemicals and domestic sewage, the introduction of non-native species, hydropower dams, and mining activities—exacerbated by the catastrophic collapse of the B1 Ore Tailings Dam at the Córrego do Feijão mine in Brumadinho in 2019. This study presents a comprehensive review of the ichthyofauna of the Paraopeba River basin, incorporating new occurrence data and analyzing fish richness and distribution, describing major threats, and suggesting conservation measures. We recorded 139 fish species across ten orders, 37 families, and 97 genera. Characiformes represented 43.2 ​% of the total richness, followed by Siluriformes (39 ​%). Among the 116 native species, 12 taxa are long-distance migrants. Non-native species accounted for 17 ​% (23 species) of the total richness. At-risk native species include Plesioptopoma curvidens (Critically Endangered), Conorhynchos conirostris (Endangered), and Pseudoplatystoma corruscans and Lophiosilurus alexandri (both Vulnerable). By integrating empirical data and compiling records from fish collections and ichthyological literature, we aimed to support the development of effective conservation and management strategies. Given the multiple stressors affecting the basin, these findings contribute to a broader understanding of the ecological dynamics and the long-term sustainability of fish populations in the region. The Paraopeba River remains a critical area for fish conservation and restoration efforts in Minas Gerais, and requires continuous monitoring, habitat restoration, and targeted conservation actions for threatened species.

摘要: Hydroelectricity is a significant source of electricity in many countries around the world. Blockage of fish migration routes is an environmental impact caused by hydroelectric power plants and schools of fish can accumulate in regions of the tailrace with no mitigation measures in place. The present work analyzed the influence of hydraulic conditions in a tailrace on fish presence in the Três Marias Hydroelectric Power Plant (Brazil). There, seven tons of fish were killed in 2007 during turbine shutdown and spillway opening. We generated a 3D hydrodynamic model in the Fluent software that compared velocity magnitude, vorticity magnitude, turbulent kinetic energy, turbulence intensity, dissipation of turbulent energy and hydraulic strain rate along the flow to the presence of Pimelodus maculatus (Mandi) and Prochilodus argenteus (Curimba) obtained during previous acoustic telemetry studies. The results indicated a higher fish presence near Turbine 1, whose values of velocity, vorticity and hydraulic strain were higher than other regions, despite similar turbine discharges. The factorial analysis for mixed data found that the combination of turbulent kinetic energy, dissipation of turbulent energy, turbulence intensity and vorticity explained 34.8 ​% of the variance, followed by the combination of hydraulic rate, vorticity and velocity at 21.3 ​%. Hydrodynamic conditions experienced by both fish species differed. For example, Mandi navigated in areas with diverse hydraulic patterns. Overall, a combination of hydraulic variables attracts both species to the Turbine 1 area, an unsafe region for shoals.

摘要: Impoundments within the Paraná River basin have significantly impacted the Upper Paraná River Floodplain (UPRF). The Itaipu Hydropower Plant, installed in 1982, removed a natural barrier, enabling fish species from the Lower Paraná River to colonize the Upper Paraná River. The completion of the Porto Primavera Dam in 1998 upstream of the UPRF facilitated the invasion of a submerged aquatic macrophyte (Hydrilla verticillata (L.f) Royle) in 2005. We aimed to assess the long-term impact of this invasive macrophyte on food chain dynamics in the UPRF, with a focus on effects to an invasive herbivore and native detritivore fish species (Schizodon borellii Boulenger, 1900 and Prochilodus lineatus Valenciennes, 1836; respectively). Impacts were assessed across three periods spanning 20 years (early 2000s, 2010s, and 2020s), capturing periods before, shortly after, and long after the macrophyte invasion. We hypothesized that the invasive macrophyte's contribution to both the green trophic pathway (energy flow from living primary producers through herbivores to predators) and the brown trophic pathway (energy flow from decomposed organic matter through detritivores to predators) would increase over time, eventually becoming the primary energy source. Using stable isotope analysis, we examined food chain energy sources, trophic niches, and trophic positions of both consumers associated with the UPRF. Our findings indicate that the herbivorous invasive fish incorporates carbon from the invasive macrophyte into the green food chain, while the native detritivore fish likely relocate from the main channel to floodplain lakes, utilizing detritus from native emerged macrophytes located only in these environments. Additionally, both species experienced an increased trophic niche shortly after invasion, possibly relating to behavioral and foraging adaptations following disturbances to the floodplain. Our study underscores how invasive species can replace native food sources, reshape local food webs, and exacerbate the ecological impacts of impoundments.