Search Results (185)

To understand the distribution characteristics of the fish community and evaluate the effectiveness of the Yangtze River fishing ban, this study selected the Fuhe River (an important tributary of the Yangtze River) as the research area. A total of 30,892 fish (belonging to seven orders, 20 families, and 92 species) were captured in the upper and middle reaches of the Fuhe River from 2022 to 2024. Among them, the Cypriniformes order accounted for the largest proportion, with nine families and 66 species, making up 71.74% of the total number of fish. According to the relative importance index, Carassius auratus was the dominant species for each sampling period and each sampling area. Moreover, the number of dominant species in the main streams was significantly higher than that in the tributaries, while the diversity of the fish community in the tributaries was significantly greater than that in the main streams. Additionally, ANOSIM revealed significant spatial differences in the fish community (p < 0.01). Cluster and NMDS analyses further divided the fish community into three groups. SIMPER indicated that the typical species of each group of fish community were basically the dominant species within that community. Furthermore, RDA indicated that potassium permanganate, ammonia nitrogen, total phosphorus, and chlorophyll a were the main water environmental factors affecting the fish community structure. Compared to the fish community before the fishing ban, the stability of the fish communities during the initial stage of the fishing ban was significantly improved, and the number of fish species also increased. Therefore, the fishing ban was beneficial for enhancing the diversity and stability of the fish community. However, compared with the composition of fish species before the fishing ban, a certain number of fish species in the upper and middle reaches of the Fuhe River were still not collected during the early stage of the fishing ban. Therefore, the ten-year fishing ban in the Yangtze River still needs to be continued and implemented. Full article

Yangtze finless porpoise (Neophocaena asiaeorientalis) is the only extant cetacean species in the Yangtze River, a national first-class protected wild animal in China, and a key indicator reflecting the health status of the Yangtze River ecosystem. Environmental changes can induce adaptive trophic responses in animal communities; thus, clarifying the dynamic interactions between fish assemblages and dietary shifts in the Yangtze finless porpoise after the fishing moratorium is critically important. In this study, fishery resources in Poyang Lake were surveyed using triple-layer composite gill nets and cage traps, with samples collected and analyzed accordingly. A total of 81 fish species belonging to 8 orders and 16 families were recorded. Following the fishing ban, the abundance of small-bodied fish species (e.g., Hemiculter bleekeri, Carassius auratus) decreased, while the proportion of piscivorous species among the top ten dominant fish increased from 40% to 60%. DNA barcoding was used to analyze gastric contents of 10 dead porpoises found post-moratorium, and the results were compared with pre-ban data. Gastric content analysis identified 11 prey taxa, and comparative analysis demonstrated that prey selectivity was closely correlated with local prey availability. Concomitant with the structural reorganization of the fish community in Poyang Lake during the early stage of the fishing ban, the Yangtze finless porpoise exhibited adaptive dietary shifts toward benthic and small-bodied fish species, suggesting a potential linkage between these ecological responses. These findings provide direct implications for formulating targeted conservation strategies for this endangered cetacean and highlight the necessity of protecting small and benthic fish populations to ensure their long-term survival. Full article

Background/Objectives: The frequent use of antibiotics has led to increasing drug resistance in Aeromonas hydrophila; therefore, there is an urgent need to develop novel antimicrobial agents to prevent and control bacterial diseases in aquaculture. Allicin E (ALE) is derived from garlic (Allium sativum L.), a plant extensively used in traditional medicine for treating infections. This study aimed to evaluate the potential of ALE against A. hydrophila, a major aquaculture pathogen, by investigating its antibacterial efficacy, mechanisms of action, and in vivo protective effects. Methods: The minimum inhibitory and bactericidal concentrations (MIC/MBC) were determined by broth microdilution. Antibacterial mechanisms were investigated through ROS detection, electron microscopy, fluorescent staining, and content leakage measurement. In vivo efficacy was evaluated in Carassius auratus gibelio by monitoring survival rates and bacterial loads, analyzing immune and antioxidant biomarkers, and histopathological analysis after A. hydrophila challenge. Results: ALE exhibited potent antibacterial activity (MIC = MBC = 8 μg/mL), achieving complete bacterial elimination within 1 h and showing a low resistance propensity. Mechanistically, ALE induced ROS accumulation, causing oxidative damage that disrupted membrane integrity and facilitated the leakage of cellular contents. In vivo, ALE significantly enhanced fish survival, reduced bacterial loads, modulated inflammatory cytokines, boosted antioxidant enzyme activities (SOD and CAT), and alleviated tissue damage. Conclusions: ALE possesses potent in vitro antibacterial activity and exerts an inhibitory effect on bacteria-induced inflammatory responses, effectively combating A. hydrophila through a multi-target mechanism and enhancing host resistance. Full article

This study evaluated the efficacy of ammonia-nitrogen-reducing biofilms (aquatic nitrifying bacteria biofilm media, a fixed-bed biofilm capable of simultaneous nitrification and denitrification) in mitigating water quality deterioration and transport-induced physiological stress in live-transported Crucian carp (Carassius auratus). In a simulated bag transport system, the application of the biofilm significantly decreased ammonia-nitrogen concentrations through enhanced nitrification, stabilized pH and dissolved oxygen dynamics, and suppressed nitrite accumulation. Correspondingly, biofilm-treated fish exhibited significantly reduced systemic stress responses, as evidenced by reduced serum cortisol, glucose, and lactate dehydrogenase concentrations, along with diminished histopathological changes in gill and liver tissues and preserved muscle fiber integrity. Regarding post-transport muscle quality, biofilm treatment delayed glycogen catabolism and lactate accumulation, maintained elevated muscle pH and water-holding capacity, reduced shear force decline, decelerated ATP hydrolysis and freshness degradation (K-value), and simultaneously suppressed lipid peroxidation and myonuclear apoptosis. These findings demonstrate that ammonia-nitrogen-reducing biofilms represent a viable biotechnological approach for maintaining water quality, mitigating stress-induced physiological disturbances, and preserving flesh quality during live fish transportation. This approach has significant potential for improving post-harvest outcomes in aquaculture logistics. Full article

Background: Aeromonas veronii is an important bacterial pathogen in crucian carp and can cause serious disease outbreaks and substantial economic losses in aquaculture. Objectives: To evaluate how A. veronii infection and its inactivated vaccine modulate immune responses in Carassius auratus. Methods: 270 juveniles were allocated into three groups: a saline-injected control group (Ctrl), a vaccination group receiving an inactivated A. veronii vaccine (Vac), and an artificial infection group (AIG) subjected to stimulation. Liver, spleen, head kidney, gill, and intestine samples were collected from fish after anesthesia. The relative transcript levels of IgM, IgD, BAFF, MHCII, CD4, BCL6, MyD88, and NF-κB were quantified. For liver transcriptome analysis, the effective library concentration was determined. And the 16S rRNA gene resulting reads of fish gill symbiotic microbiota were processed for downstream bioinformatic analysis. Results: The results showed that the Vac achieved an RPS of 73.33%, and vaccination significantly upregulated multiple immune-related genes in different fish organs. With BAFF transcription across organs emerging as a robust sentinel readout. The Pearson correlation coefficient (r) of BAFF between other genes were all ≥0.8. GO and KEGG enrichment analyses indicated that AIG had more DEGs than Vac (5885 vs. 4008) and Ctrl (6910 vs. 6178), respectively. Some genes in AIG revealed significant over-representation of immune pathways, such as BCL6, MyD88, and NF-κB. The fish gill microbiota comprised a diverse set of low-abundance taxa, the phylum level was dominated by Proteobacteria and Fusobacteriota across all groups; whereas, the Vac group remained broadly closer to the Ctrl group in overall composition. Conclusions: These results indicated marked post-challenge immune–metabolic coupling in the liver, and suggested coordinated immunophysiological interplay between the liver and the spleen. Gill microecology of symbiotic bacteria was affected by vaccination or challenge reactions, which in turn affects the health of the gills or the organism itself. Full article

The deterioration of water quality is associated with an increased disease risk, although the exact mechanism remains unclear. This study investigated the infection dynamics of cyprinid herpesvirus 2 (CyHV-2) in crucian carp (Carassius auratus gibelio) subjected to varying nitrite stress levels. A control group and three CyHV-2-infected groups exposed to nitrite concentrations of 0, 5, and 10 mg/L were set up. Results indicated that nitrite exposure caused a dose-dependent reduction in survival rates and decreased viral loads in the spleens of surviving fish. Nitrite stress elevated malondialdehyde (MDA) levels and glutathione peroxidase (GPx) activity, while reducing superoxide dismutase (SOD) and catalase (CAT) activities in the liver. Hepatic cytokine analysis revealed early peaks in tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), alongside delayed response of interferon γ (IFN-γ) and interleukin 10 (IL-10), indicating impaired anti-inflammatory regulation. In the kidney, nitrite stress amplified immune gene expression, characterized by the upregulation of tlr5 (Toll-like receptor 5) and nf-κb (nuclear factor κB) and the inhibition of iκκβ (inhibitor of NF-κB kinase subunit β), leading to prolonged NF-κB signaling. This was associated with a marked upregulation of il-1β and il-8 (interleukin 8), alongside a delayed ifn-γ response. The combination of nitrite stress and CyHV-2 infection exacerbated oxidative damage and triggered a maladaptive immune response, thereby accelerating disease progression. Full article

Prophylactic antibiotic use in high-density ornamental aquaculture aims to mitigate infections, yet it is hypothesized to induce severe gut microbiome dysbiosis, contributing to high post-purchase mortality of goldfish purchased from retail stores by end consumers. This study utilized 16S rRNA gene amplicon sequencing, a rapid and high-resolution tool to characterize gut bacterial communities in six goldfish (Carassius auratus) sourced from antibiotic-intensive retail market in Hong Kong SAR, China. Diversity metrics were compared to unexposed reference controls and experimentally antibiotic-exposed cyprinid groups from published datasets. Market-sourced goldfish showed a profound collapse in alpha diversity (mean Shannon index 0.107 ± 0.141), far lower than controls (typically 2.0–4.5) and experimental groups (1.06–4.34). The microbiota exhibited extreme oligodominance by Cetobacterium and Vibrio, with near-total loss of beneficial commensal taxa. Principal coordinates analysis (PCoA) revealed distinct clustering, indicating fundamental and likely irreversible microbial restructuring. These findings show that chronic antibiotic exposure in ornamental supply chains induces a depauperate microbiome state, compromising host resilience and physiological homeostasis during environmental transitions. This dysbiosis provides a microbiological explanation for widespread post-purchase die-off, highlighting a major animal welfare and biosecurity concern. High-throughput sequencing offers quick, in-depth microbiome health assessment, essential for developing interventions to improve husbandry and reduce antimicrobial reliance in the global ornamental fish trade. Full article

This study examines the histological, ultrastructural, and immunohistochemical features of the lip skin of the goldfish (Carassius auratus, Linnaeus, 1758), a sensory-rich region that plays an essential role in feeding and environmental perception. Our findings highlight the coexistence and close association of immune, epithelial, and sensory cells within the epidermis and dermis. For the first time in goldfish, intraepidermal macrophages, eosinophilic granular cells, rodlet cells, Merkel cells, and several specialized sensory structures—neuromasts, taste buds, and tuberous-like sensory units—were simultaneously identified within the same integumentary field. Quantitative morphometry demonstrated a high density of eosinophilic granular cells, rodlet cells, and neuromasts per unit epithelial area, reinforcing the functional specialization of the goldfish lip as a sensory–immune interface. Immunohistochemical markers (CK20, S100, CD68, CD64, CD117, and E-cadherin) were applied as complementary tools to describe phenotypic labeling patterns. These findings are interpreted cautiously as supportive evidence consistent with epithelial, neural-associated, stromal, and immune cell distributions observed morphologically. Transmission electron microscopy further uncovered fine structural details such as synapse-like contacts in taste buds and Merkel cells, dense-core granules in eosinophilic granular cells, and telocyte–nerve fiber associations in the dermis. By integrating cellular, structural, and immunohistochemical perspectives, this study provides a novel descriptive reference for the goldfish lip skin as a region characterized by the close spatial association of sensory and immune-related elements, underscoring its value as a model for vertebrate cutaneous biology and neuroimmunology. Full article

Objectives: This study aimed to investigate the regulatory effects of dietary carvacrol on intestinal micro biota composition, serum metabolic profiles, and their association with increased resistance to Aeromonas hydrophila in Pengze crucian carp. Methods: Juvenile fish (5.63 ± 0.35 g) were randomly allocated into two experimental groups: a control group (CK) fed a basal diet and a treatment group (CA) supplemented with 600 mg/kg microencapsulated carvacrol. Following an 8-week feeding trial, nine specimens per group were sampled for venous blood and intestinal tract collection. Remaining individuals were subjected to a 12-h A. hydrophila challenge prior to identical sample collection. Results: Key findings revealed that carvacrol supplementation induced significant microbial modulations, notably reducing Firmicutes abundance while enhancing Cetobacterium populations by 33.25% compared to controls. Post-challenge analysis demonstrated marked declines in intestinal microbial diversity indices (Observed ASV, Chao1, ACE, and PD whole tree) in the CK group, whereas the CA group maintained stable microbial diversity. Pathogenic genera including Aeromonas, Shewanella, and Vibrio showed significant proliferation in challenged controls, contrasting with maintained microbial homeostasis in carvacrol-fed specimens. Serum metabolomic profiling identified the most significantly altered metabolic pathways associated with carvacrol administration: glycerophospholipid metabolism, linoleic acid metabolism, arachidonic acid metabolism, α-linolenic acid metabolism, GPI-anchor biosynthesis, and autophagy-animal pathways. Conclusions: Our results demonstrate that dietary carvacrol may reinforce intestinal microbial barrier function by optimizing beneficial microbial composition and reducing the proportion of pathogens, and modulate immune-related metabolic pathways critical for host defense, which might be involved in enhanced disease resistance. Full article

Non-native fish invasions are important drivers of freshwater biodiversity and ecosystem function loss. In this study, we compared the trophic niches of four non-native (Rhinogobius giurinus, Hemiculter leucisculus, Hypomesus nipponensis, and Tachysurus fulvidraco) and one native fish species (Carassius auratus) from April 2022 to December 2023 in Erhai Lake, a typical plateau lake on the Yunnan–Guizhou Plateau, China. We analyzed δ¹³C and δ¹⁵N from 766 fish samples and calculated 103 SEA_b values across species, seasons, and lake regions. Stable isotope analyses revealed pronounced trophic niche differentiation between non-native and native fishes. Non-native species exhibited wider niche width (4.81 ± 0.48), lower overlap (24.43 ± 1.57), and higher within-group dispersion (2.69 ± 0.07), indicating greater trophic plasticity. In contrast, native fishes showed narrower niches (2.72 ± 0.32), higher overlap (37.32 ± 4.21), and lower plasticity (1.68 ± 0.08). Moreover, non-native and native fishes adopted contrasting trophic strategies: individual fitness increased with niche expansion in non-native fishes, whereas it declined in native fishes. Multiple linear analyses further indicated significant competitive effects of non-native fishes on native species’ niches, suggesting that niche expansion in native fishes represents a passive response to intensified competition rather than an adaptive strategy. Overall, the high trophic plasticity of non-native fishes and their asymmetric effects on native species imply a high risk of food web reorganization in Erhai Lake. These results provide guidance for the sustainable management of Erhai Lake, balancing invasive species control with native fish conservation. Our results underscored the importance of incorporating trophic interactions into invasion management and native fish conservation. Full article

Yi’an Reservoir is located on a major tributary of the Baoquan River and hosts abundant aquatic resources, with Cyprinus carpio, Carassius auratus, and Hemiculter leucisculus as the dominant fish species. Water quality parameters significantly shape fish gut microbiota, which in turn plays a crucial role in host physiological functions. This study aimed to characterize the water quality parameters in Yi’an Reservoir and identify the microbial communities in both the aquatic environment and fish guts (C. carpio, C. auratus, and H. leucisculus) through 16S ribosomal RNA sequencing. The objective was to examine the associations of water quality parameters and aquatic environmental microbiota with the assembly of gut microbial communities in fish inhabiting this reservoir system. The water quality parameters showed significant site-specific differences, of which temperature and dissolved oxygen were highest at Location B, while pH was highest at Location A. The Cyanobium_PCC-6307 was identified as a major differentially abundant taxon at the genera level across different sampling sites. Furthermore, the gut microbiota of the same fish species exhibited substantial variation across different sampling sites. Redundancy analysis identified distinct environmental drivers at each location. Specifically, pH, conductivity, and total dissolved solids (TDS) showed positive correlations with the gut microbiota at Location A. In contrast, temperature, dissolved oxygen (DO), and the environmental abundance of Cyanobium PCC-6307 were positively correlated with the gut microbiota at Locations B and C. This study provides important insights for the conservation and management of aquatic resources in reservoir ecosystems. Full article

Allotetraploid fish produced by distant hybridization are valuable germplasm for the mass production of sterile triploids. The allotetraploid crucian–carp hybrid (4nAT, 4n = 200) is derived from the intergeneric cross between a female red crucian carp (Carassius auratus red var., 2n = 100) and a male common carp (Cyprinus carpio L., 2n = 100). However, after 33 successive generations, this lineage faces a critical bottleneck in maintaining male fertility. The present study aimed to develop new biomarkers for testicular development and characterize the associated functional gene expression profile in 4nAT. Following whole-genome resequencing and selection signature analysis of 15 male 4nAT individuals from each of the high-development group (HDG) and low-development group (LDG), ZSWIM7 (Zinc Finger SWIM-Type Containing 7), a gene implicated in reproductive development, was selected as a candidate for further fertility association studies. Seven SNPs were screened in the coding region of ZSWIM7 of 70 4nAT males; among these, SNP3 (c.23T/C) exhibited a significant correlation between genotypes and testicular development: individuals with the CT genotype showed a higher gonadosomatic index (1.17 ± 0.68 vs. 0.65 ± 0.50) and greater counts of mature spermatozoa (2537.67 ± 283.95 vs. 341.56 ± 121.66) compared to those with the TT genotype. Further quantitative PCR and immunofluorescence assays demonstrated that ZSWIM7 was highly expressed in the testis and specifically localized to the nuclei of early meiotic primary spermatocytes. Collectively, these results establish ZSWIM7 as a promising biomarker for 4nAT testicular development, offering a potential molecular tool for maintaining male fertility in allotetraploid fish breeding. Full article

Microplastics are pervasive in aquatic environments; however, their impacts on aquatic organisms at environmentally relevant concentrations remain poorly understood, particularly under field conditions. To address this gap, we employed high-throughput sequencing to assess these impacts under both field and laboratory conditions using crucian carp (Carassius auratus) as a model organism. Following a 4-week exposure in situ, the abundance of intestinal microplastics slightly increased from an initial level of 55.00 ± 59.73 items/fish to 72.67 ± 27.50 items/fish (p > 0.05). Accordingly, a total of 3036 differentially expressed genes (DEGs) were identified in the hepatic transcriptome, with notable enrichment in pathways related to lipid metabolism and oxidative stress. Furthermore, a positive correlation between intestinal microplastic abundance and exposure concentration was observed in fish following a 2-week laboratory exposure to polyamide (PA), with intestinal burdens ranging from 7.50 ± 3.54 to 367.50 ± 17.68 items/fish. The number of DEGs in the hepatic transcriptome, ranging from 41 to 380 items, demonstrated a nonlinear relationship with microplastic levels. Furthermore, these DEGs were primarily enriched in pathways associated with lipid metabolism and oxidative stress, including the PPAR signaling pathway (ko03320) and fatty acid degradation (ko00071). This suggests that microplastics at environmental levels may have detrimental effects on organisms through perturbations in lipid metabolism and oxidative stress. As expected, these findings provide essential insights for evaluating the ecological risks linked to microplastic pollution at environmental levels. Full article

Background/Objectives: Carvacrol, a major active component of oregano oil and common feed additive, has been widely studied for its effects on fish growth, immunity, and intestinal health. But its transcriptional/metabolic impacts on fish liver remain unclear. This study investigated these effects in Pengze crucian carp (Carassius auratus var. Pengze). Methods: Fish were fed a basal diet (control) or basal diet supplemented with 10% microencapsulated carvacrol (600 mg/kg) for 56 days; liver samples were analyzed via transcriptomics and metabolomics. Results: Transcriptomic analysis revealed 482 differentially expressed genes (DEGs) in the liver of Pengze crucian carp following carvacrol supplementation, with 158 upregulated and 324 downregulated genes. Functional annotation highlighted enrichment in translation, signal transduction, amino acid metabolism, and posttranslational modification pathways. GO analysis further identified key processes, including carboxylic acid transport, tRNA aminoacylation, and mitochondrial nucleoid function, while KEGG pathways were implicated in amino acid biosynthesis, lipid metabolism (e.g., alpha-linolenic acid), and insulin signaling. Metabolomic profiling identified 679 significantly altered metabolites, including 113 upregulated and 566 downregulated ones. Among these, upregulated compounds like L-asparaginyl-L-lysine (Log₂FC = 4.36) and 2′-Deoxyadenosine-5′-diphosphate (Log₂FC = 4.31) are linked to nucleotide metabolism, and downregulated peptides (e.g., Ala-Phe-Tyr-Arg) suggesting modulated protein turnover. Joint omics analysis revealed convergent pathways in glycerophospholipid metabolism, aminoacyl-tRNA biosynthesis, and autophagy. Notably, the chaperone gene dnaja3b was correlated strongly with neuroactive metabolites (e.g., normetanephrine), potentially implicating carvacrol in stress response regulation. Conclusions: Our findings demonstrate that carvacrol modulates liver gene expression and metabolic profiles, primarily influencing amino acid and lipid metabolism pathways, autophagy, and stress responses. The observed correlations between dnaja3b and specific metabolites offer mechanistic insights into the action of carvacrol in fish liver. Full article

This study evaluated the effects of short-term depuration under different salinity levels on the muscle nutritional composition and quality of Carassius auratus gibelio, aiming to provide guidance for enhancing the value of farmed crucian carp. A total of 240 fish (450 ± 50 g) were reared in recirculating aquaculture systems at salinities of 0‰ (S0), 3‰ (S3), 6‰ (S6), and 9‰ (S9) for 0 (D0), 5 (D5), and 10 days (D10). Dorsal muscle samples were analyzed for proximate composition, amino acids, fatty acids, flavor-related nucleotides, geosmin, and volatile compounds. Short-term depuration significantly improved muscle protein content, total amino acids, and umami amino acids. Culturing at 6‰ salinity for 10 days enhanced crude protein, total amino acids, umami amino acids, and lipid indices associated with cardiovascular benefits, while 9‰ salinity for 5 days increased crude lipid, total umami amino acids content, and the essential amino acid index (EAAI). Geosmin content decreased under moderate salinity but tended to accumulate at higher salinities. Amino acid scoring identified lysine, methionine, and cysteine as limiting under certain conditions, indicating a need for supplementation. Overall, short-term salinity depuration effectively improves muscle nutritional composition, fatty acid profiles, and flavor attributes, offering a practical approach to producing higher-value C. auratus gibelio with enhanced health benefits and consumer appeal. Full article