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In this study, we produced a population of gynogenetic mrigal carp (Cirrhinus mrigala , GMCJ) through artificial gynogenesis using UV-inactivated white crucian carp spermatozoa. The GMCJ exhibited a faster growth rate and strong resistance to low temperatures, surviving natural winter conditions with temperatures below 10 °C. To gain a deeper insight into GMCJ's molecular response to acute cold stress (a decrease in water temperature from 26 °C to 14 °C within 1 h at a rate of 0.2 °C/min), we conducted a comparative analysis of the histology and transcriptomics of the brain-liver axis. Transmission electron microscopy of the heart tissues revealed that acute cold stress result in widened myofilament spacing, along with enlarged, deformed mitochondria that developed vacuoles and ruptured. We identified differentially expressed genes (DEGs) in the brain (2463 upregulated and 3288 downregulated genes) and liver (1210 upregulated and 1224 downregulated genes). Analysis of the DEGs' correlations indicated that major pathways involved in immunity, disease, metabolism, and growth were active and interconnected. KEGG functional analysis showed that the most enriched pathways in the brain-liver axis involved the regulation of the glucagon pathway, PI3K-Akt signaling pathway, and herpes simplex infection. Numerous genes associated with the nervous-endocrine system were activated, suggesting a coordinated response of the brain-liver axis to acute stress. These findings enhance our understanding of how farmed, particularly gynogenetic fish respond to acute cold stress. • GMCJ fish show strong resistance to low temperatures. • Immunity and metabolism genes active under acute stress. • Brain-liver axis coordinates response to acute stress. [ABSTRACT FROM AUTHOR]

Crucian carp (Carassius auratus) is one of the main freshwater cultured fish species in China, and its species degeneration and diseases outbreak for aquaculture brings great economic losses. However, the blood single cellular morphology and molecular identification still needs further investigation in fish. Here, the blood parameters, single-cell types and shapes, physicochemical indexes and phagolysosome (PL)-related gene expression analysis of C. auratus were examined. The results showed that four single-cell types of blood cells, including hematopoietic progenitor cells (HPCs), red blood cells (RBCs), proerythrocytes (PEs) and platelets (PLTs) were identified by pseudotime trajectory analysis in the whole blood and kidney, respectively. The involvement in the PL signaling pathway was significantly observed in GSEA enrichment analysis, and their expression distribution (e.g., CD63, ITGB2, CXCR4b, MMP2, MHCI uka, B2ML, CD74a, FTH1a, COX8b, COX7a2) were evaluated in various tissues. A protein-protein interaction network analysis was performed on the highly expressed cellular markers and co-expressed genes. Moreover, CaCD63 gene cloning and expression, and molecular docking interaction were presented with the integrin (ITGB2) and chemokine receptor (CXCR4b). Overall, this study firstly revealed the molecular marker features of blood cells and provided a valuable reference for further function verification in cyprinid fish. • Blood cell and physicochemical indexes analysis were examined in crucian carp C. auratus. • Four types of single cells (HPCs, RBCs, PEs, and PLTs) were described in detail. • Molecular docking interaction of CD63 with ITGB2 and CXCR4b were explored for the first time. • Expression distribution of 17 phagolysosome-related genes was evaluated in various tissues. [ABSTRACT FROM AUTHOR]

To follow up field observations in the Chornobyl Exclusion Zone (ChEZ), a series of controlled model aquarium experiments were conducted to determine the uptake and depuration rates of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) in fresh water, varying in temperature from 5 to 27 °C, with daily feeding rates of 0–1.5 % fish weight day−1. In the present study, the 137Cs uptake rates in muscle tissues directly from water, 0.05–0.09 day−1 at temperatures of 5–27 °C, were significantly lower than previously reported for fish fed under natural conditions in contaminated lakes within the ChEZ. The rate of 90Sr uptake in bone tissues of silver Prussian carp varied from 0.055 day−1 at a water temperature of 5 °C and feeding rates ≤0.15 % fish weight day−1 to 1.5 ± 0.2 day−1 at a temperature of 27 ± 1 °С and at the highest tested feeding rate of 1.5 % day−1. The rate of decrease of 137Cs concentration in muscle tissues was k b = 0.0028 ± 0.0004 day−1 (T 1/2 = 248 ± 35 days) at the lowest water temperature tested (5 °С). At water temperatures between 13 and 26 °С and a feeding rate of 0.15 % day−1, the rate increased to k b = 0.0071–0.0092 day−1 (T 1/2 = 75–99 days). The rates of decrease of 90Sr activity concentration in bone tissues at water temperatures between 22 and 25 °С and a feeding rate of 0.5 % day−1 were k b = 0.004–0.0014 day−1, and the associated biological half-life T 1/2 ranged 50–160 days, respectively. The present work supported conclusions related to the main pathways of 137Cs and 90Sr uptake by silver Prussian carp, and demonstrated the usefulness of combining field and laboratory uptake and depuration experiments. • The 137Cs uptake rate by fish from water is 5–100 times lower than from contaminated food. • The 137Cs uptake rate by fish from water increased at high water temperatures. • The 90Sr uptake rate by fish from water is much higher than from contaminated food. • The 90Sr uptake rate from water increased with increasing water temperature and feeding rate. • The rates of decrease in 137Cs and 90Sr concentrations increase due to biodilution. [ABSTRACT FROM AUTHOR]

Compared to α-Fe 2 O 3 solid NCs and α-Fe 2 O 3 nucleoshell NCs, α-Fe 2 O 3 hollow NCs-based TMA sensor exhibits high sensitivity, rapid response-recovery time and excellent selectivity in detecting TMA for indirectly assessing Carassius auratus freshness, which will make remarkable contribution for guaranteeing food safety and quality. [Display omitted] • Construction of an efficient TMA gas sensor by α-Fe 2 O 3 hollow nanocubes. • High response, rapid response-recovery time and good selectivity of the sensor. • Feasibility of Carassius auratus quality evaluation by detecting TMA. • Linear relationship between sensor's response and the storage time of the fish. Trimethylamine (TMA) is an organic amine with strong pungent smell which is an indicator gas for evaluating fish freshness according to the international standard. In this work, as-synthesize α-Fe 2 O 3 solid nanocubes (NCs), α-Fe 2 O 3 nucleoshell NCs and α-Fe 2 O 3 hollow NCs were used as sensing material to develop an outstanding TMA gas sensor. The response of the α-Fe 2 O 3 hollow NCs sensors towards 20 ppm TMA at 230 ℃ was 6.3. Meanwhile, these sensors showed exceptional response/recovery time, low limit of detection, great selectivity, and outstanding linear relationship. Furthermore, the analysis of gases released during the decomposition of Carassius auratus (0–10 days) was conducted, which demonstrated the assessment of TMA by α-Fe 2 O 3 hollow NCs sensor can evaluate the freshness of Carassius auratus. Such a novel sensor signifies the outstanding application potential in efficient gas-sensing properties of TMA, which will make the tremendous contribution for Carassius auratus product evaluation in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fabrication of hydrogel using collagen extracted from crucian carp skin. • Improved mechanical properties of collagen hydrogel through PC method. • Luteolin was successfully loaded into collagen hydrogel. • Luteolin-incorporated hydrogel scaffold promoted wound healing. In clinical practice, wound care has always been challenging. Hydrogels play a key role in facilitating active wound recovery by absorbing exudates, maintaining moisture, and alleviating pain through cooling. In this study, type I collagen was isolated from the skin of crucian carp (Carassius carassius) and verified by amino acid analysis, FTIR, and SDS-PAGE. By adopting a new approach, luteolin was added to collagen hydrogels in situ after being dissolved in an alkaline solution. XRD and SEM confirmed the luteolin was incorporated and entirely distributed throughout the hydrogel. The plastic compression improved the young's modulus of hydrogel to 15.24 ± 0.59 kPa, which is adequate for wound protection. The drug loading efficiency was 98 ± 1.47 % in the selected formulation. The luteolin-incorporated hydrogel enabled regulated drug release. We assessed the cytotoxicity using MTT and live-dead assays, as well as examined the hemocompatibility to determine the biocompatibility of the hydrogel. In vivo experiments showed that the hydrogel with luteolin had the highest wound closure rate (94.01 ± 2.1 %) and improved wound healing with granular tissue formation, collagen deposition, and re-epithelialization. These findings indicate that this efficient drug delivery technology can accelerate the process of wound healing. [ABSTRACT FROM AUTHOR]

Benthic freshwater cyanobacteria have the potential to produce toxins. Compared with more extensively studied plankton species, little is known about the impact of harmful benthic cyanobacteria on aquatic organisms. As demersal fish are usually in direct contact with benthic cyanobacteria, it is important to understand their interactive effects. This study investigated the physio-chemical responses of two demersal fish (Xenocypris davidi and Crucian carp) after exposure to benthic Oscillatoria (producing cylindrospermopsin, 2 × 106 cells/mL) for 7 days. Interestingly, benthic Oscillatoria had less adverse effects on X. davidi than C. carp. The two demersal fish effectively ingested Oscillatoria , but Oscillatoria cell sheathes could not be fully digested in C. carp intestines and led to growth inhibition. Oscillatoria consumption induced oxidative stress and triggered alterations in detoxification enzyme activities in the X. davidi liver. Superoxide dismutase (SOD) and glutathione reductase (GR) activities significantly increased in the C. carp liver , but catalase (CAT) and detoxification enzymes glutathione S-transferase (GST) and glutathione (GSH) activities were insignificantly changed. This suggested that C. carp may have a relatively weak detoxification capacity for toxic Oscillatoria. Oscillatoria ingestion led to more pronounced liver pathological changes in C. carp , including swelling, deformation, and loss of cytoskeleton structure. Simultaneously, fish consumption of Oscillatoria increased extracellular cylindrospermopsin concentration. These results provide valuable insights into the ecological risks associated with benthic cyanobacteria in aquatic ecosystems. [Display omitted] • Oscillatoria consumption induced oxidative stress in both X. davidi and C. carp liver. • Oscillatoria cell sheathes could not be fully digested in C. carp intestines. • C. carp has relatively weak detoxification capacity for toxic Oscillatoria. • Oscillatoria ingestion led to more pronounced liver pathological changes in C. carp. • Fish predation behavior on Oscillatoria increased extracellular cylindrospermopsin concentration. [ABSTRACT FROM AUTHOR]

The application of cold shock to inhibit the extrusion of the second polar body in fertilized eggs is one of the main methods to induce triploid in diploid fish. In this study, we originally planned to induce hexaploid by this method in tetraploid carp. However, among the surviving offspring, we observed only 50.7% tetraploid and 49.3% diploid individuals, which could potentially result from either androgenetic diploids or gynogenetic diploids. The absence of irradiation and the high proportion of diploids attracted us. However, the lack of sex-specific markers for tetraploid carp, makes it difficult to determine their origin. Fortunately, we also carried out the cross of yellow carp (Cyprinus carpio yellow var., 2n, ♀) × tetraploid carp (♂) and red crucian carp (Carassius auratus red var., 2n, ♀) × tetraploid carp (♂) with cold shock inhibiting the second meiosis, diploid offspring have also been found, and whether they have undergone gynogenesis or androgenesis can be judged based on phenotype and genotype. In terms of phenotypes, the key phenotypes of two diploids, such as the whisker length, number of lateral scales, and presence of melanin, are consistent with tetraploid carp. In terms of genotypes, through single-copy nuclear gene cloning and fluorescence in situ hybridization (FISH), it is supported that both diploids are androgenetic offspring. In addition, 14.9% of tetraploid offspring were found in red crucian carp (♀) × tetraploid carp (♂) with cold shock inhibiting the second meiosis. By the above-mentioned means of detection, it was found that they were created by inhibiting the extrusion of the second polar body of the fertilized eggs. From this it will be seen that the application of cold shock before the extrusion of the second polar body of fertilized eggs cause not only polyploidy, but also the elimination of both second polar body and female nucleus. Previous studies have found that cold shock can induce lethal androgenetic haploids in diploid fish, but these androgenetic diploid fish produced by tetraploid carp sperm were surviving. We summarize the mechanism behind the above phenomenon, which is mainly related to meiosis occurring at the edge of the cell membrane. Cold shock may disrupt the function of the spindle, resulting in the simultaneous retention or extrusion of female nucleus and second polar body. This study will provide valuable insights into androgenesis, polyploidization, and hybridization in fish genetic breeding. • Androgenetic diploids were induced from tetraploid carp sperm by cold shock without irradiating the eggs. • New-type allotetraploids were induced in the cross between male tetraploid carp and female diploid carp by cold shock. • Nuclear gene cloning is suitable for qualitative analysis of the genetic composition of hybrids, but not for quantitative analysis. [ABSTRACT FROM AUTHOR]

The effects of different concentrations of sodium bicarbonate (0 g/L, 1 g/L, 2 g/L, 3 g/L) on Hefang crucian carp (HCC) were studied. H&E staining, oil red O staining, scanning electron microscopy, transmission electron microscopy, 16S rDNA sequencing, transcriptomic analysis and other techniques were used to observe the pathological changes of intestinal and liver tissues, and detect the changes of intestinal flora and liver gene expression. The main findings are as follows: It was found that the WGR and SGR of the three treatment groups was significantly higher than that of the CK group (p < 0.05). Intestinal H&E staining results showed that the number of goblet cells and the width of submucosa gradually increased with the increase of carbonate concentration. The results of intestinal scanning electron microscopy showed that the roughness of intestinal villi increased slightly with the increase of carbonate concentration. The analysis of populations with large differences among groups treated with sodium bicarbonate of different concentrations found that the relative abundance of Lachnospiraceae varied greatly. LPS levels in the serum, intestinal tract and liver tissue were detected. The results showed that LPS content in MCA and HCA groups was significantly higher than that in CK group (p < 0.05). The expression of claudin 12, 7, c and occludin genes in HCA group and MCA group was significantly lower than that in CK group in intestinal (p < 0.05). The ALT, AST, T-CHO, TG, HDL C, ACC, ACS, CPT-1, HL, LPL and FAS content in HCA group was significantly higher than that in CK group in liver (p < 0.05). The liver was damaged by oil red O staining and transmission electron microscopy. Compared with the control group, the enrichment of steroid biosynthesis is the highest number of DEGs in the HCA group. The iron death pathway and autophagy pathway in HCA group were significantly different from those in CK group (p < 0.05). In summary, this study elucidates that carbonate exposure alters the gut microbiota homeostasis of HCC, leading to intestinal inflammation and increased mucosal barrier permeability, promoting LPS synthesis and absorption, subsequently entering the liver through the gut-liver, increasing liver autophagy and iron death, inducing lipid metabolism disorders, and causing liver injury. In summary, carbonate exposure may cause intestinal microbial disturbance and intestinal injury, and induce liver autophagy and iron death and lipid metabolism disturbance, leading to liver injury • Carbonate stress inhibited the growth of Hefang crucian carp through enterohepatic axis pathway. • Carbonate stress can destroy intestinal flora homeostasis of Hefang crucian carp. • Carbonate stress induced lipid metabolism disorder in the liver of Hefang crucian carp. [ABSTRACT FROM AUTHOR]

Two fish species from the middle reaches of the Yangtze River, China, were sampled to investigate the occurrence, tissue distribution, age-dependent accumulation and ecological risk assessment of 24 organophosphorus flame retardants (OPFRs). Seventeen OPFRs were detected in tissue samples with a total concentration ranging from not detected (ND) to 1092 ng g−1 dw. Cl-OPFRs were predominant in all tissues (mean: 145 ng g−1 dw, median: 72.9 ng g−1 dw) and the concentrations of OPFRs in brain were the greatest (crucian carp: 525 ng g−1 dw, silver carp: 56.0 ng g−1 dw) compared with the other three organs (e.g., liver, muscle and gonad). Furthermore, the total concentrations of OPFRs in crucian carp tissues were significantly greater than those in silver carp (P < 0.01). Age-dependent accumulation of OPFRs was observed in the two fish species, but the accumulation profiles in the two fish species were different. Ecological risk assessment demonstrated that both fish species were at medium to high risk, and TDCIPP was a main contributor (>50%). [Display omitted] • OPFRs were widely detected in fish from the Yangtze River. • Brain was a main accumulation organ of OPFRs. • OPFRs caused age-dependent bioaccumulations in wild fish. [ABSTRACT FROM AUTHOR]

[Display omitted] • A QuEChERS method was developed to provide good analytical results for teicoplanin (TEC) and ramoplanin (RAM) residues in aquatic products. • Compared to conventional adsorbents, chitosan has a relatively good purification ability for the targets. • This study shows low matrix effect for all targets in different aquatic products such as crucian carp, turbot, shrimp and so on. A QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method was developed to provide good analytical results for teicoplanin (TEC) and ramoplanin (RAM) residues in aquatic products. The analytes was extraction from aquatic product samples using chitosan in the QuEChERS procedure. Compared to conventional adsorbents, chitosan has a relatively good purification ability for the targets. The matrix effects of aquatic products, such as crucian carp, carp, silver carp, tilapia, mandarin fish, turbot, shrimp, sea cucumber and so on, were evaluated by high performance liquid chromatography coupled to triple-quadrupole tandem mass spectrometry. Throughout the validation experiments, the limits of detections and quantifications ranged from 0.4 ∼ 0.8 μg kg−1 and 1.0 ∼ 3.0 μg kg−1, respectively. Calibration curves showed correlation coefficient values higher than 0.998 in range between 1 and 100 μg kg−1. The recoveries ranged from 89.8 % to 110.0 % with relative standard deviation less than 7.2 % in nine typical aquatic products. The method shows low matrix effect (-18.5 %∼-2.6 %) for all targets in different aquatic products. The proposed methods proved to be reliable, effective and enables rapid determination of large batch samples, indicating its good applicability for detection and monitoring of TEC and RAM residues in aquatic products. [ABSTRACT FROM AUTHOR]

Antibacterial and active packaging materials have gained significant research attention in response to the growing interest in food packaging. In this investigation, we developed hydrogel packaging materials with antibacterial and antioxidant properties by incorporating chitooligosaccharide (COS) and fish skin gelatin (FSG) nanofiber membranes, which readily absorbed water and exhibited swelling characteristics. The nanofiber membranes were fabricated by electrospinning technology, embedding COS within FSG, and subsequently crosslinked through the Maillard reaction facilitated by the addition of glucose. The behavior of conductivity, viscosity, and surface tension in the spinning solutions was analyzed to understand their variation patterns. Scanning electron microscopy (SEM) results revealed that the crosslinked COS/FSG nanofiber membranes possessed a uniform yet disordered fiber structure, with the diameter of the nanofibers increasing as the COS content increased. Remarkably, when the COS content reached 25 %, the COS/FSG nanofiber membranes (CF-C-25) exhibited a suitable fiber diameter of 437.16 ± 63.20 nm. Furthermore, the thermal crosslinking process involving glucose supplementation enhanced the hydrophobicity of CF-C-25. Upon hydration, the CF-H-25 hydrogel displayed a distinctive porous structure, exhibiting a remarkable swelling rate of 954 %. Notably, the inclusion of COS significantly augmented the antibacterial and antioxidant properties of the hydrogel-based nanofiber membranes. CF-H-25 demonstrated an impressive growth inhibition of 90.56 ± 5.91 % against E. coli , coupled with excellent antioxidant capabilities. In continuation, we performed a comprehensive analysis of the total colony count, pH, TVB-N, and TBA of crucian carp. The CF-H-25 hydrogel proved highly effective in extending the shelf life of crucian carp by 2–4 days, suggesting its potential application as an edible membrane for aquatic product packaging. [Display omitted] • Nanofibers composed of COS/FSG were synthetized via the electrospinning technique. • Hydrogel was prepared by water absorption swelling of nanofibers after Maillard reaction. • COS/FSG nanofiber-based hydrogel was fabricated for food packaging. • COS/FSG nanofiber-based hydrogel have significant antibacterial and antioxidant properties. [ABSTRACT FROM AUTHOR]

IL-22 is a critical cytokine of epithelial mucosal barrier. In humans, IL-22 signals through a heteroduplex receptor consisting of IL-22R and IL-10Rβ. In fish, IL-22 and its receptors homologues have been cloned in a number of species, however, no studies have been reported how the receptors are involved in IL-22 transduction. For this purpose, in this study we identified IL-22 and its soluble receptor IL-22BP and transmembrane receptors IL-22RA1 and IL-10R2 in Carassius cuvieri × Carassius auratus red var. (named WR-IL-22, WR-IL-22BP, WR-IL10R2 and WR-IL22RA1, respectively). WR-IL-22, WR-IL-22BP, WR-IL10R2 and WR-IL22RA1 were relatively conserved in the evolutionary process, sharing the same conserved domains as their higher vertebrate homologues. When the fish were infected with the Aeromonas hydrophila , the expression of WR-IL-22, WR-IL-22BP, WR-IL10R2 and WR-IL22RA1 were significantly induced in the gut. The co-IP assay showed that WR-IL-22 not only interacted with WR-IL-22BP, but also with WR-IL10R2 and WR-IL22RA1. When introduced in vivo , WR-IL-22 activated the JAK1-STAT3 axis and protected the gut mucosa from A. hydrophila infection. However, overexpression of WR-IL-22BP or knockdown of transmembrane receptors WR-IL10R2 and WR-IL22RA1 significantly inhibited the activation of WR-IL-22-mediated JAK1-STAT3 axis and promoted bacterial colonization in the gut. These results provided new insights into the role of IL-22 and its receptors in the gut mucosa barrier and immune response in teleost. • mRNA expression of WR-IL-22 was significantly induced by bacterial challenge. • WR-IL-22 interacted with WR-IL-22BP, WR-IL10R2 and WR-IL22RA1. • WR-IL-22 enhanced host gut barrier during Aeromonas hydrophila infection. [ABSTRACT FROM AUTHOR]

Aeromonas veronii has serious implications for food safety and the aquaculture industry. The iron uptake system can effectively regulate the life activities and pathogenicity of microorganisms, and Fur is one of the key proteins. In this experiment, we constructed the Δ fur mutant strain of A. veronii TH0426 using the pRE112 suicide plasmid and the C- fur complementary strain using the pBBR1-MCS generalized host expression plasmid to research the effects of fur gene on the biological function and mechanisms of virulence regulation of TH0426. It was found that when the fur gene was deleted, the polar flagella of TH0426 was disrupted and the biofilm formation ability was significantly reduced, with consequent changes in motility, flagellation-related gene expression, drug resistance, and tolerance. Transcriptome analysis of TH0426 wild-type and Δ fur mutant showed that fur gene could directly or indirectly regulate bacterial flagella assembly, antibiotic resistance, growth and metabolism. In the pathogenic test, compared with the TH0426 wild-type, Δ fur significantly reduced the cytotoxicity to EPC cells at 30 min, 1 h and 2 h, reduced the adhesion and invasion ability to EPC cells by 2.38-fold (P < 0.001), increased LD 50 of zebrafish by 58.33-fold (P < 0.001) and decreased bacterial load at 12 h, 24 h, and 48 h. Meanwhile, the result of C- fur was higher than that of Δ fur and lower than that of the TH0426 wild-type in all experiments. In summary, the fur gene is essential for flagellar assembly and biofilm formation and is able to indirectly affect some of the biological properties and animal pathogenicity of TH0426. This research helps to explain the function of the fur gene of the iron uptake system and its role in the pathogenesis of animal. • fur gene can directly regulate the assembly of polar flagella in A. veronii TH0426. • fur gene could directly regulate the biofilm formation of A. veronii. • Deletion of fur gene could significantly reduce the pathogenicity of A. veronii to crucian carp and zebrafish. • Deletion of fur gene can affect multiple metabolic pathways in A. veronii. [ABSTRACT FROM AUTHOR]

Establishing beneficial intestinal microbiota using autochthonous probiotics is a promising approach for disease control and growth regulation during fish rearing. Therefore, it is crucial to identify indigenous probiotics with high application potential in aquaculture. In this study, we screened Bacillus coagulans BC1, a strain with strong application potential. After a comprehensive safety assessment, diets containing varying doses of BC1 were formulated and administered to crucian carp. Subsequently, a feeding experiment was conducted to evaluate non-specific immune response, intestinal structure, microbiota, and challenge protection rate. The results demonstrate that oral supplementation of BC1 can lead to tissue-dependent upregulation of various serum immune enzymes and IgM levels, while significantly enhancing the expression of IL-1β , IL-10 , TNF-α , and TGF-β in various organs of crucian carp (p < 0.05). The BC1 diet effectively promoted intestinal morphology in crucian carp and improved resistance to Aeromonas veronii TH0426 infection. Intestinal microbiota analysis revealed that the oral addition of BC1 significantly changed the intestinal microbial community structure of crucian carp but did not clearly affect intestinal microbial diversity. Oral administration of BC1 significantly improved the relative abundance of Cetobacterium in the intestines of crucian carp; reduced the abundance of opportunistic pathogens such as Bacteroides , Vibrio and Aeromonas and effectively regulating the nutrient metabolism in intestinal microbiota. These results indicate that BC1 could regulate immune function, effectively improving the intestinal morphology and intestinal flora structure and function of crucian carp, and therefore is a potential candidate strain for aquatic feed additives. • B. coagulans strain BC1 with strong application potential in aquatic feed additive was obtained by in situ screening. • Oral BC1 effectively enhanced the non-specific immunity of crucian carp juvenile. • BC1 diet could regulate the structure and function of intestinal flora of crucian carp juvenile. [ABSTRACT FROM AUTHOR]

• The metabolism of diet As was investigated in food fish during chronic exposure • Arsenic adaption involved reduced As bioaccumulation and increased As biotransformation • The bioavailability of dietary arsenite was lower than that of arsenate • Arsenite was largely formed in fish muscle at earlier stage of arsenate exposure Dietary uptake is the major way that inorganic arsenic (iAs) enters into benthic fish; however, the metabolic process of dietborne iAs in fish muscle following chronic exposure remains unclear. This was a 40-day study on chronic dietborne iAs [arsenite (AsIII) and arsenate (AsV)] exposure in the benthic freshwater food fish, the crucian carp (Carassius auratus), which determined the temporal profiles of iAs metabolism and toxicokinetics during exposure. We found that an adaptive response occurred in the fish body after iAs dietary exposure, which was associated with decreased As accumulation and increased As transformation into a non-toxic As form (arsenobetaine). The bioavailability of dietary AsIII was lower than that of AsV, probably because AsIII has a lower ability to pass through fish tissues. Dietary AsV exhibited a high potential for transformation into AsIII species, which then accumulated in fish muscle. The largely produced AsIII considered more toxic at the earlier stage of AsV exposure should attract sufficient attention to human exposure assessment. Therefore, the pristine As species and exposure duration had significant effects on As bioaccumulation and biotransformation in fish. The behavior determined for dietborne arsenic in food fish is crucial for not only arsenic ecotoxicology but also food safety. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Rahnella aquatilis is widely recognized as an opportunistic pathogen of fish, but molecular detection and diagnostic techniques for it remain to be developed. In a previous study, we isolated the pathogenic R. aquatilis strain KCL-5 from diseased crucian carp Carassius auratus and identified it as a new fish pathogen causing enteritis and septicemia. Here, we describe novel real-time quantitative PCR (RT-qPCR) and loop-mediated isothermal amplification (LAMP) assays for the rapid and sensitive detection of R. aquatilis. Specific RT-qPCR and LAMP primers were developed for the outer membrane protein (OmpA) gene. Their reaction systems were optimized using the recombinant plasmid pMD18-T containing the OmpA gene and their specificities were confirmed using various bacterial fish pathogens including Aeromonas hydrophila , A. veronii , A. allosaccharophila , Yersinia ruckeri , Vibrio vulnificus , V. alfacsensis, Providencia rettgeri , and R. aquatilis. The sensitivities of the RT-qPCR and LAMP assays were further evaluated using serial dilutions of the positive recombinant plasmid pMD18-T/ OmpA. Both the RT-qPCR and LAMP assays were able to reliably detect the presence of R. aquatilis with high accuracy and a specificity of 100%. The lowest detection limits of the RT-qPCR and LAMP assays were 2.3 copies/μL and 2.3 × 101 copies/μL, respectively. To the best of our knowledge, this is the first report of RT-qPCR and LAMP methods for R. aquatilis detection, and provides a means for its rapid detection and diagnosis in fish. • Development of qPCR assay for detection of R. aquatilis in fish. • Establishment of LAMP assay for detection of R. aquatilis with MDL of 2.3 × 101 copies/μL. • The qPCR and LAMP methods were firstly established for the rapid detection of R. aquatilis. • Analysis of bacterial loads was performed for R. aquatilis infection in fish. [ABSTRACT FROM AUTHOR]

Whilst the hybrids of F1 generations usually experience heterosis for fitness-related traits (including the resistance to parasites), post-F1 generations, due to Dobzhansky–Muller genetic incompatibilities, express numerous disadvantageous traits (including susceptibility to parasites). Genetic disruption in hybrids may also result from the broken system of cyto-nuclear coadaptation. Maternal backcrosses (having parents with the same mtDNA) and paternal backcrosses (having parents with different mtDNA) have the same nuclear genetic compositions, but differ in cytoplasmic genetic elements, affecting their viability and survival. Spring viraemia of the carp virus (SVCV), a disease with a serious economic impact in aquacultures, affects almost exclusively cyprinids, primarily common carp (Cyprinus carpio), and causes high mortality, whilst gibel carp (Carassius gibelio) is a less susceptible species. Our study was focused on the transcriptome profile analysis of head kidney to reveal differential gene expression in highly susceptible common carp, weakly susceptible gibel carp, and hybrid lines, hypothetizing that the patterns of differential gene expression will reflect hybrid heterosis in F1 generations and hybrid breakdown in backcrosses and F2 generations. We expected the differences in differential gene expression between maternal and paternal backcrosses to be in line with the hypothesis of broken cyto-nuclear coadaptation. The pattern of differential gene expression revealed from the transcriptomic analysis of head kidney was linked to the resistance or susceptibility to SVCV infections in two pure species, C. gibelio and C. carpio , and their various generations of inter-specific hybrids. We evidenced hybrid heterosis for F1 generations of hybrids, mostly reflected by similarity in the down-regulation of differentially expressed genes classified within the viral infection disease category. High hybrid breakdown was documented throughout the transcriptomic analysis for paternal backcross generations and F2 generation of hybrids, confirming the broken system of cyto-nuclear coadaptation in those post-F1 generations. This evidence may support the role of intrinsic selection acting against inter-specific hybridization in freshwater fish. • Spring viraemia of carp is a disease with a serious economic impact for aquacultured fish. • We performed transcriptome profile analysis of the head kidney to reveal differential gene expression (DEG) in highly susceptible common carp, weakly susceptible gibel carp, and hybrid lines, hypothesizing that the patterns of differential gene expression reflect heterosis in F1 hybrids and breakdown in backcrosses and F2 hybrids. • DEG was linked to the resistance or susceptibility to SVCV infections in pure species and their various generations of hybrids. • We evidenced the similarity in DEGs between F1 hybrids and weakly susceptible gibel carp supporging hybrid heterosis for F1 hybrids. • Hybrid breakdown was suggested for paternal backcross generations and F2 generation of hybrids, confirming the broken system of cyto-nuclear coadaptation. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the hepatotoxic effects of trichlorfon on crucian carp (Carassius carassius) and the attenuating effects of a synbiotic combination of Cetobacterium somerae and Astragalus polysaccharide on hepatotoxicity. Results showed that trichlorfon did indeed induce hepatotoxicity in crucian carp and the synbiotic reversed this hepatotoxicity caused by trichlorfon. The synbiotic increased TC, TG, LDL-C, ALT and AST levels and decreased serum HDL-C levels caused by trichlorfon. H&E and Oil Red O staining demonstrated that the synbiotic ameliorated liver damage and abnormal lipid accumulation. The activity of antioxidant enzymes (T-SOD, CAT, GSH-Px) in the liver was also enhanced by the administration of the synbiotic. The supplementation of the synbiotic also increased the level of short-chain fatty acids in the intestine. In addition, the synbiotic balanced the gut microbial composition, leading to a reduction in the abundance of potentially pathogenic bacteria and an increase in the abundance of bacteria producing short-chain fatty acids. In conclusion, these findings indicate that trichlorfon can induce hepatotoxicity in crucian carp, whereas synbiotics can regulate gut microbiota, promote the growth of beneficial bacteria and increase the production of SCFAs, and alleviate trichlorfon-induced liver injury. [Display omitted] • Trichlorfon can cause hepatotoxicity in Crucian carp. • Administration of the synbiotic alleviated trichlorfon-induced liver injury and lipid accumulation. • Administration of the synbiotic modulated gut microbiota and increased short-chain fatty acid levels. [ABSTRACT FROM AUTHOR]

Activity concentrations of 90Sr in fish in lakes located within the Chornobyl Exclusion Zone (ChEZ) reach 100 kBq kg−1, which is several thousand times higher than the permissible level in Ukraine (35 Bq kg−1). This study was conducted in the natural conditions of the ChEZ to determine the effectiveness of keeping radioactively contaminated fish in "clean" water to reduce the 90Sr content of their muscle tissue, as previously shown in short-term laboratory experiments. It was found that transferring tench (Tinca tinca (Linnaeus, 1758)) from Lake Glubokoye one of the most contaminated lakes in the ChEZ, to a cage in the "clean" Lake Starukha for 45 days did not lead to a significant decrease in 90Sr content in both bone and muscle tissues. Establishing permissible levels of 90Sr concentration only in fish fillet, and not in the whole fish body (with bone tissue), is appropriate for human radiation protection, since the retention factors of 90Sr treatment for boiled bone tissue of crucian carp from the Chornobyl exclusion zone are less than 0.01, and up to 97% of strontium is contained in bone tissue. [Display omitted] • No reduce of 90Sr content in contaminated fish when kept in "clean" water for 45 days. • Less than 1% of 90Sr is transferred to broth during boiling of fish bone tissue. • Current Ukrainian permissible levels of 90Sr in fish products need to be revised. • Long-term experiments are needed to study ways to remove 90Sr from fish tissues. [ABSTRACT FROM AUTHOR]

TNFα is one of important cytokines belonging to TNF superfamily, which can exhibit a pleiotropic effect in immune modulation, homeostasis as well as pathogenesis. However, its immunoregulatory function on mucosal immunity in fish gut are still unclear. In this study, we aimed to investigated the immunoregulatory role of TNFα1 in midgut of white crucian carp (WCC). WCC-TNFα1 sequence and its deduced structure were firstly identified in WCC. Then, tissue-specific analysis revealed that high-level WCC-TNFα1 expression was detected in gill. After Aeromonas hydrophila and lipopolysaccharide (LPS) stimulated, increased trends of WCC-TNFα1 expressions were detected in immune-related tissues and cultured fish cells, respectively. WCC anal-intubated with WCC-TNFα1 fusion protein showed the increased levels of edema and fuzzy appearance in impaired villi, along with atrophy and reduction of goblet cells (GC). Moreover, the expression levels of tight junction (TJ) genes and mucin genes were consistently lower than those of the control (P < 0.05). WCC-TNFα1 treatment could sharply decrease antioxidant status in midgut, while the expression levels of caspase (CASP) genes, unfolded protein response (UPR) genes and redox response genes increased dramatically. Our results suggested that WCC-TNFα1 could exhibit a detrimental effect on antioxidant and mucosal immune regulation in midgut of WCC. • The deduced structure and expression patterns of WCC-TNFα1 were firstly reported in WCC. • WCC receiving WCC-TNFα1 perfusion showed a dramatically reduced expressions of tight junction and mucin. • WCC-TNFα1 perfusion induced apoptotic activation but decreased antioxidant status in midgut [ABSTRACT FROM AUTHOR]

Acclimatization of certain ectothermic vertebrates to winter conditions is associated with reduced energy consumption (winter dormancy). Principally, this may be achieved by reducing movement activity, depression of basal cellular functions, or by switching from aerobic to anaerobic energy production to sustain low energy consumption during anoxia. Therefore, we determined standard (SMR), routine (RMR) and anoxic (AMR) metabolic rates in summer- (SumA; 20 °C) and winter-acclimatized (WinA; 2 °C) crucian carp (Carassius carassius), an anoxia-tolerant teleost fish. At 20 °C, RMR was 39% lower in WinA than SumA fish (p < 0.05), indicating reduced movements in winter. SMR, measured for the first time in crucian carp, was 45% lower in WinA than SumA fish at 10 °C (p < 0.05), indicating significant reduction of energy consumption in vital cellular processes. At 2 °C, AMR - measured from ethanol production- was 78% and 97% of the SMR and RMR levels at the same temperature, respectively. The current study revealed that the winter dormancy in anoxia-tolerant crucian carp is achieved in 3 different steps: (1) by active reduction of SMR, possibly in anticipation of seasonal anoxia, (2) acute Arrhenius Q 10 effect that slows SMR as well as RMR, and (3) direct response to the absence of oxygen (AMR). Furthermore, the anoxic energy production was strongly dependent on body mass with scaling exponents of −0.335 and − 0.421 for WinA and SumA fish, respectively. [Display omitted] • In crucian carp, the metabolic winter acclimatization involves 3 steps down in energy consumption. • Routine metabolic rate was 39% lower in winter- than summer-acclimatized fish. • Standard metabolic rate was 45% lower in winter- than summer-acclimatized fish. • The anoxic energy production was strongly dependent on fish body mass. [ABSTRACT FROM AUTHOR]

Our study aimed to test whether fluoxetine impairs learning in fish and whether this potential impairment is reversible. Learning efficiency, with no aversive stimuli, of the Carassius carassius was analysed under different pharmaceutical conditions: (i) fish cultured without antidepressant (control), (ii) fish exposed to fluoxetine for 21 days (fluoxetine), and (iii) fish exposed to fluoxetine for 21 days and then cultured without fluoxetine for another 21 days (recovery). We exposed animals to environmental concentrations (360 ng L−1) of antidepressant. The learning rate was measured by timing how long it took the individual fish to find food and start feeding, six days in a row. The control and recovery fish took significantly less time to start eating over the six days. Control fish start eating 14 times faster than the fluoxetine fish. Fluoxetine can significantly affect learning and 21-day recovery period is not enough to fully restore the original learning abilities. [Display omitted] • Low concentrations of fluoxetine affects fish learning in reduced stress conditions. • Learning efficiency after six days is different for control and fluoxetine fish. • Control fish reached food and start eating 14 times faster than the fluoxetine fish. • 21-day recovery period is not enough to fully restore original learning abilities. [ABSTRACT FROM AUTHOR]

It has been reported that antibiotic enrofloxacin can impair reproductive function of mammals, induces multi-generational oscillatory effects on reproduction of Caenorhabditis elegans , and disturbes endocrine system in grass carp. This study aims to explore the effect of short-term enrofloxacin exposure on sex steroid hormones biosynthesis in Carassius auratus var. Pengze through assessing the contents of growth hormone (GH), thyroid hormone 4 (T 4), estradiol (E 2) and testosterone (T) in plasma, and investigating sex steroid hormones biosynthesis based on targeted metabonomics analysis, and determining expression level of some important genes, gonadotropin-releasing hormone (gnrh), gonadotropin hormone 1-β (gth1-β), gonadotropin hormone 2-β (gth2-β) and cyp19a1a in hypothalamus-pituitary-ovary axis (HPOA). We found that short-term exposure of enrofloxacin disordered contents of E 2 and T in plasma of fish determined by ELISA detection, T content elevation and E 2 content decline, which was confirmed by the following data from targeted metabonomics analysis of plasma. The metabonomic results showed that both T and its upstream intermediate products during the process of sex steroid hormones biosynthesis in fish were increased significantly, but E 2 content was decreased markedly. At the exposure 24 h of enrofloxacin, expression of gnrh in hypothalamus, gth1-β and gth2-β in pituitary were promoted. Meanwhile GH and T 4 contents in plasma, two inducers of sex steroid hormones synthesis, were augmented, which indicated that sex steroid hormones biosynthesis was improved. However cyp19a1a expression in ovary was repressed, and content of estriol (E 3) was upregulated. These data suggested that enrofloxacin promoted sex steroid hormones biosynthesis and conversion of E 2 to estriol (E 3), but inhibited the conversion of T to E 2. Finally, content of E 2 was declined sharply. Animal specific antibacterial enrofloxacin is widely detectable in aquatic ecosystem, exposure of the agent can induce adverse effects on plants and animals. This study firstly evidenced induction of disruption of sex steroid hormones by enrofloxacin in fish, which indicates enrofloxacin is an endocrine disruption compound that can induce endocrine disruption of animals, including fish. [Display omitted] • Short-term enrofloxacin exposure promotes secretion of GH and T 4 in crucian carp. • Enrofloxacin inhibits biotransformation of T to E 2 , inducing accumulation of T. • Enrofloxacin promotes E 2 metabolism to E 3 , resulting in reduction of E 2. • Enrofloxacin promotes expression of gnrh and gth genes. [ABSTRACT FROM AUTHOR]

Fish in lakes situated within the Chornobyl exclusion zone have been highly contaminated since the accident and have not been utilized as food for humans. In the present study, field experiments with less-contaminated silver Prussian carp (Carassius gibelio (Bloch, 1782)) caged in contaminated lake within the Chornobyl exclusion zone was performed from June to October 2021 to investigate the effectiveness of clean feed containing potassium ferric hexacyanoferrate (KFCF) KFe[Fe(CN) 6 ], a kind of Prussian Blue as a countermeasure to reduce 137Cs accumulation in fish. The addition of clean feed containing 0.1% or 1% KFCF resulted respectively in 2.4 ± 0.4 or 4.2 ± 0.7 times lower activity concentration of 137Cs in muscle tissue of the carp compared to control fish with clean feed without KFCF and in 7–16 or 12–27 times lower activities compared to fish without additional clean feeding. After 18 weeks exposure, 137Cs levels in all the caged fish except for the control group were below the European permissible level (600 Bq kg−1) for consumption. In contrast, KFCF did not affect the intake of 90Sr in fish, although additional feed increased the growth rate and thereby accumulation in bone tissues. Hence, the use of clean feed containing KFCF is judged to be an effective and inexpensive countermeasure to reduce the 137Cs contamination of edible fish muscles. [Display omitted] • The reduction factor of 137Cs ranged from 7 to 27 for fish given clean feed containing potassium ferric hexacyanoferrate (KFCF). • Application of clean feed decreased the 137Cs activity concentration in muscle only by a factor of 2.6 ± 0.3 during summer. • Application of clean KFCF diet affected neither the intake of 90Sr in fish nor fish growth. • Field experiments are needed to identify efficient countermeasures for fish. [ABSTRACT FROM AUTHOR]

TNFα is a multifunctional cytokine that can modulate immune homeostasis and promote cellular regulation in mammals, but the crucial role of TNFα in fish gut remained unclear. The current study aimed to evaluate the immunoregulatory function of TNFα2 on gut barrier breach by A. hydrophila and systemic pathogenesis in gut and liver of WR (White crucian carp ♀ × red crucian carp ♂). WR-TNFα2 encoded 232 amino acid residues and showed a high-level of WR-TNFα2 expression in spleen. After A. hydrophila and lipopolysaccharide (LPS) stimulated, elevated levels of WR-TNFα2 expressions were detected in immune-related tissues and cultured fish cells, respectively. Gut perfusion with WR-TNFα2 alone could alter antioxidant status, increase extrinsic apoptosis as well as promote inflammatory response in midgut, causing severe injury of epithelial barrier. Moreover, WR-TNFα2-treated midgut exhibited a decline of mucosal protection against invasive A. hydrophila , which could elevate bacterial burden in tissues, aggravate tissue injury as well as attenuate immune activation. Our results suggested that WR-TNFα2 could exhibit a detrimental effect on gut barrier defense against A. hydrophila infection and dysregulate immune response in midgut and liver of hybrid crucian carp. • The predicted structure and expression patterns of TNFα2 were firstly reported in WR. • WR-TNFα2 altered antioxidant status and increased extrinsic apoptosis in midgut. • WR-TNFα2 facilitated bacterial infection by impairing gut barrier and then exacerbated liver lesion. [ABSTRACT FROM AUTHOR]

Based on the formation of fertile allotetraploid fish (4nJB, 4n = 148) derived from female Carassius cuvieri (JCC, 2n = 100) × male Megalobrama amblycephala (BSB, 2n = 48), an improved Japanese white crucian carp (IJCC) was obtained by mating female 4nJB and male 4nJB, and thus far, the population of IJCC has reached the fifth generations (F 1 –F 5). The purpose of the present study was to comparatively investigate the biological characteristics of the IJCC lineage (F 1 –F 5) and their original female parent JCC. The results of DNA content and chromosome numbers showed that the IJCC lineage was diploid with 100 chromosomes. For morphological characteristics, it appears that IJCC-F 1 has smaller head and a higher body width than that of JCC, and some countable traits as well as the ratio of measurable traits were significantly different (P < 0.05) between these two fish. With the passing of generations, the appearance of the IJCC lineage has been stable. Regarding reproductive characteristics, the fecundity, sperm volume, sperm density, fertilization rate and hatching rate were not significantly different (P > 0.05) between the JCC and IJCC lineages, indicating that the reproductive capacity of the IJCC lineage was similar to that of the JCC. Furthermore, the growth performance showed that the average weight of IJCC-F 1 and IJCC-F 5 was significantly greater (P < 0.05) than that of JCC both at 6 months and 1 year of age. The good fertility of the IJCC lineage ensures the multigeneration utilization of its advantage, and the IJCC lineage has significant value in aquatic applications. • The improved IJCC lineage was established derived from JCC (♀) × BSB (♂). • The produced IJCC lineage grows faster than JCC. • The reproductive capacity of IJCC lineage was similar to that of JCC. [ABSTRACT FROM AUTHOR]

[Display omitted] • We utilized eDNA to study riverine fish communities across the Qinghai-Tibet Plateau. • A total of 90 fish species were detected, belonging to 34 families and 79 genera. • Fish communities were directly affected by watershed characteristics. • This study implied potential species invasion on the Qinghai-Tibet Plateau. The Qinghai-Tibet Plateau (QTP) serves as the source of many large rivers in Asia, and also serves as a natural habitat for rare wildlife and a genetic reservoir for plateau species. The exceptional ecological environment of the QTP has fostered diverse fish species. However, due to climate change and human activities, fish species in this area are facing serious threats, while large spatial scale investigation is a big challenge. Environmental DNA (eDNA) metabarcoding, as an innovative monitoring technology, offers a simple, fast, and environmentally friendly approach to explore fish communities on the QTP. This study utilized eDNA technology to assess the diversity, composition, and potential environmental influences of riverine fish communities across the QTP. A total of 90 fish species were identified belonging to 79 genera, 34 families, and 18 orders. The dominant species were Schizothorax chongi , Gymnocypris przewalskii , Carassius carassius , and Botia striata. PCoA and ADONIS indicated significant differences among fish community in different river basins of the Qinghai-Tibet Plateau. Canonical correspondence analysis (CCA) revealed that the ratio of SRP to TP, average NDVI, average elevation, and proportion of bare land significantly influenced the distribution of fish community. This study provided a novel monitoring method and insight for fish communities and implied potential species invasion on the QTP. [ABSTRACT FROM AUTHOR]

The pentraxin family is an evolutionarily conserved group that plays an important role in innate immunity. C-reactive protein (CRP) and serum amyloid P component (SAP) are classical members of the short pentraxins and are known to be the major acute phase proteins. In this work, we have cloned a novel pentraxin fusion protein, WR-PTXF, from Carassius cuvieri × Carassius auratus red var. In fish, the biological function of PTXF is essentially unknown. For this purpose, we report the identification and analysis of WR-PTXF and elucidate its role in the antibacterial innate immunity. WR-PTXF contains 224 amino acids and shares 79.8% and 23.0% sequence identities with crucian carp CRP and SAP, respectively. Blast analysis shows that WR-PTXF and goldfish PTXF had the highest similarity (97.3%). WR-PTXF is expressed in multiple tissues and is upregulated by Aeromonas hydrophila infection. WR-PTXF contains a short pentraxin domain and recombinant WR-PTXF protein (rWR-PTXF) can bind the A. hydrophila in a concentration-dependent manner. Further, rWR-PTXF displays apparent bacteriostatic activity against A. hydrophila in vitro by enhancing the uptake of the bound bacteria by host phagocytes. When introduced in vivo , rWR-PTXF not only protects the gut mucosa but also limits the colonization of A. hydrophila in systemic immune organs. Consistently, knockdown of WR-PTXF significantly promotes bacterial dissemination in the tissues of host. These results indicate that WR-PTXF is a classic pattern recognition molecule that exerts a protective effect against bacterial infection. • mRNA expression of WR-PTXF was significantly induced by bacterial challenge. • WR-PTXF enhanced host gut barrier. • WR-PTXF exhibited bactericidal activity to Aeromonas hydrophila infection. [ABSTRACT FROM AUTHOR]

Due to its water solubility and wide applicability, enrofloxacin hydrochloride (EH) may enter aquatic ecosystems and cause negative effects on aquatic organisms. This study aimed to explore toxicological effects via serological changes and neurotoxicity, which were induced by EH exposure in crucian carp (Carassius auratus var. Pengze). The drug residues in brain tissue and protein content in serum were determined to analyze serological changes. Alterations in brain tissue structure and function, cerebral microvessels permeability, and the expressions of gene and protein regarding blood-brain barrier (BBB) were studied to reflect the neurotoxicity. Employing a validated high-performance liquid chromatography (HPLC) method, EH residues could be detected at various time-points throughout the experiment. Enzyme-linked immunosorbent assay (ELISA) showed that EH increased the levels of S100B, NSE and GFAP proteins in serum. Additionally, there was a significant positive correlation between serum S100B, NSE protein contents and EH residues (P < 0.05). Hematoxylin and eosin (H&E) staining revealed brain damage from EH exposure by the formation of vacuoles in brain glial cells, pyknosis of the nucleus, and a decrease in cell population density. Transmission electron microscope (TEM) revealed morphological changes in microvessels and condensation of astrocyte nucleus. Evans blue (EB) permeability test visualized an obvious increase in cerebral microvessels leakage. The real-time quantitative PCR (qPCR) results indicated that EH up-regulated the mRNA expression levels of S100B, NSE and GFAP, down-regulated the mRNA expression levels of P-gp, ZO-1, Occludin and Claudin-5. The Western blot (WB) results demonstrated increased NSE and GFAP protein expressions, decreased P-gp and Occludin protein expressions following EH exposure in brain, in consistent with the gene expressions, respectively. In conclusion, these findings indicated that EH brought about marked rise in serum biomarker levels and disrupted the central nervous system (CNS) of crucian carp. These data would help elucidate the mechanism underlying EH-induced neurotoxicological effects. [Display omitted] • S100B and NSE could be used as biomarkers for evaluating brain damage caused by EH. • EH remodeled histological and ultrastructural structures of brain tissue. • EH triggered the leakage of cerebral microvessels. • EH disrupted the expression of BBB-related genes and proteins in crucian carp. [ABSTRACT FROM AUTHOR]

Transforming growth factor β1 (TGFβ1) is a polyfunctional cytokine with important roles in growth, differentiation and immune function in various animals. In this study, PCR, bioinformatics, real-time quantitative PCR, prokaryotic expression, protein purification and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-TOF-MS) were applied to investigate the structural features and function of TGFβ1-b in crucian carp. The complete coding sequence (CDS) of TGFβ1-b was 1134 bp in length and was submitted to GenBank (ID: MH473141). TGFβ1-b encoded a putative protein of 377 amino acids and included a signal peptide consisting of 22 amino acids. TGFβ1-b was relatively conservative in fish and distant from mammals in terms of evolutionary relationship. TGFβ1-b was found to be expressed in various tissues, with the highest expression in the kidney. The expressions of TGFβ1-b in muscle, heart and liver were increased with the addition of Rhodopseudomonas palustris , Bacillus subtilis and Enterococcus faecium at 30 days (p < 0.01). While, the expressions of SMAD2 , SMAD3 and SMAD7 were also up-regulated with the addition of R. palustris at 20 days (p < 0.01). The expression of TGFβ1-b could be affected by time and group factors (p < 0.05). Moreover, the expression vector TGFβ1-b -pDE2 was successfully constructed. Prokaryotic expression indicated that a 43 kDa target protein was obtained after induction with 1.5 mM isopropyl-beta-D-thiogalactopyranoside (IPTG) for 3.5 h at 37 °C for 200 r/h. The activities of alkaline phosphatase and lysozyme in injection TGFβ1-b protein group (ITg) and feeding broken bacterial liquid group (BTg) were significantly increased at 24 h (p < 0.01). And the activities of superoxide dismutase in ITg were significantly increased at 36 h (p < 0.01). Besides, the expressions of heat shock protein 30 and heat shock protein 47 in ITg and BTg were significantly increased (p < 0.01). Whereas, the expression of interleukin-11 was significantly reduced (p < 0.01). These results indicated that TGFβ1-b protein might play a role in immunity of crucian carp. [ABSTRACT FROM AUTHOR]

This study aimed to explore the effects of Astragalus membranaceus polysaccharide (AMP) on the growth and innate immunity of crucian carp (Carassius auratus). Crucian carps were randomly divided into a control group (fed with basal diet) and three AMP groups (received basal diet supplemented with 50, 100 and 150 mg/kg AMP). After 60 days of culture, the crucian carps from each group were weighed, and their immune indexes were measured. Another batch crucian carps from each group was injected with 0.15 ml of 107 CFU/ml Aeromonas hydrophila. The body weight gain, feed conversion rate, specific growth rate and digestive enzyme activity of the crucian carps in the low and middle doses of AMP groups were higher than those in the control group. The AMP groups had significantly higher survival rate and alkaline phosphatase level but lower glutamic–oxaloacetic transaminase, glutamic-alanine transaminase and serum bacteria number compared with the control group. The optimal dose of dietary AMP required for the maximum growth of crucian carp was 100 mg/kg. These results showed that AMP could promote the growth of crucian carps, improve their disease resistance and thus may be developed as a dietary supplement. [ABSTRACT FROM AUTHOR]

The present study investigated dietary Enteromorpha prolifera polysaccharide (EPP) on the growth performance, body composition and non-specific immunity of crucian carp Carassius auratus. Crucian carps with body weight of 51.24 ± 4.08 g were randomly divided into five groups: one group was fed with basic diet, while the other four groups were fed with diets containing 20, 40, 60 and 80 g/kg EPP. After 60 days of feeding, dietary administration of 40 g/kg EPP increased the body weight gain rate, feed conversion ratio, specific growth rate, body crude protein content, intestine digestive enzyme activities, serum lysozyme activity, acid phosphatase activity, alkaline phosphatase activity, complement 3 level, superoxide dismutase activity and catalase activity and decreased body fat content and serum total cholesterol, triacylglycerol, alanine aminotransferase activity and glutamic oxaloacetic transaminase activity compared with those of the control group. All levels of EPP improved the resistance to Aeromonas hydrophilia compared with the control group. The results indicated that EPP could promote the growth of crucian carp and improve their disease resistance and may be used as a dietary supplement for crucian carp. [ABSTRACT FROM AUTHOR]

Organophosphate flame retardants (OPFRs) can rapidly biotransform into two types of metabolites in biota: (1) organophosphate diesters (DAPs) and (2) hydroxylated OPFRs (HO-OPFRs). Therefore, the levels of parent OPFRs alone are not sufficient to indicate OPFR pollution in biological organisms. This study analyzed 12 OPFR metabolites, including 6 DAPs and 6 HO-OPFRs, in a typical freshwater food chain consisted of crucian carp, catfish, mud carp, snakehead, and oriental river prawn. The total concentrations of OPFR metabolites were comparable to those of parent OPFRs, and ranged from 0.65 to 17 ng/g ww. Bis(2-butoxyethyl) 3′-hydroxy-2-butoxyethyl phosphate (14%–77%), di- n -butyl phosphate (DNBP) (6.7%–24%), bis(1-chloro-2-propyl) phosphate (BCIPP) (0.7%–35%), and 1-hydroxy-2-propyl bis(1-chloro-2-propyl) phosphate (BCIPHIPP) (6.0%–24%) were the major OPFR metabolites. Various aquatic species exhibited significant differences in their OPFR metabolite/parent ratios (MPR) (p < 0.05), indicating varying biotransformation potentials of different organisms for various OPFRs. The growth-independent accumulation of tri- n -butyl phosphate (TNBP), tris(chloro-2-propyl) phosphate (TCIPP), triphenyl phosphate, and 2-ethylhexyl diphenyl phosphate in mud carps could be explained by their biotransformation potential. A significant negative correlation was found between the concentration of bis(2-butoxyethyl) phosphate and δ15N values (p < 0.05), with a calculated trophic magnification factor (TMF) of 0.66. Significant positive correlations were observed between BCIPP and TCIPP (R2 = 0.25, p < 0.05), as well as between DNBP and TNBP (R2 = 0.30, p < 0.01), implying that these two DAPs could be used as biomarkers to quantitatively assess TCIPP and TNBP contamination in wild aquatic organisms. [Display omitted] • DAPs and HO-OPFRs had high detection frequencies and comparable levels to parent OPFRs. • Biotransformation affected the species- and growth-dependent accumulation of OPFRs. • BBOEP underwent trophic dilution in the aquatic food chain. • DAPs and HO-OPFRs can be used as biomarkers for OPFR monitoring. [ABSTRACT FROM AUTHOR]

Black carp (Mylopharyngodon piceus) is an important fishery resource and the main breeding target in China. Due to the lack of an assay of immunoglobulin M (IgM) antibodies in black carp, there is no effective method to evaluate adaptive immune response, which limits immunological studies and vaccine development. The present study used mAbs (monoclonal antibodies) against serum IgM of grass carp as capture antibodies. The results of Western blot analysis indicated that these antibodies had strong affinity and specificity to IgM heavy chain in black carp serum and were used to detect the antibody titer, optimize the conditions, perform a sensitivity test, and develop an indirect ELISA (enzyme-linked immunosorbent assay) to detect specific IgM antibodies in the serum. This detection method has good specificity and is effective only for grass carp (Ctenopharyngodon idella) and black carp and not for crucian carp (Carassius aumtus), silver carp (Hypophthalmichthys molitrix), bighead carp (Hypophthalmichthys nobilis), mandarin fish (Siniperca chuatsi), black bream (Megalobrama skolkovii), or yellow catfish (Pseudobagrus fulvidraco). The lowest antigen detection level was 0.05 μg/ml. The error of experimental repetition in the same sample was 1.61–4.61%. The levels of specific IgM in black carp serum were steadily increased after immunization, peaked on day 28, and then slowly decreased. Indirect ELISA can be applied to detect the changes in specific antibodies in black carp serum. Moreover, indirect ELISA provides a convenient and reliable serological detection method for immunological research and evaluation of immune effects of a vaccine in black carp. • The mAb (monoclonal antibodies) targeting IgM of grass carp were used to detect IgM in black carp serum. • An indirect ELISA was established to detect specific IgM in black carp serum. • Grass carp and black carp have similar IgM heavy chain segments. • The indirect ELISA was used to study the changes of specific IgM in serum of black carp. [ABSTRACT FROM AUTHOR]

Perfluorocaproic acid (PFHxA), a short-chain substitute for the emerging contaminant perfluorinated compounds, has been detected in the aquatic environment. However, its aquatic toxicity and health risk assessment are mainly unknown. In this study, we compared the toxic doses of 0 mg/L, 5 mg/L, 15 mg/L, 45 mg/L and 135 mg/L on the pathological damage to tissue sections, antioxidant indexes and inflammatory factor expressions in liver, spleen, kidney, Prosogaster, Mid-gut, Hid-gut as well as the changes of IgM, C3, C4, LZM, GOT, GPT in serum of crucian carp. We determined the response of the intestinal microbial community to PFHxA stress by 16S. The results showed that the growth performance of crucian carp was slowed with the increase of PFHxA dose, which caused different degrees of damage to the tissues. Meanwhile, the indexes of SOD, GSH-Px, T-AOC, ACP, AKP and LZM in each tissue were reduced, and the indexes of IgM, C3, C4 and LZM in serum were reduced. The levels of MDA, GOT and GPT in tissues and GOT and GPT in serum were promoted. In addition, IL-1β, TNF-α, NF-KB, and KEAP-1 in each tissue increased compared with the control group. The levels of IL-10, Nrf2, CAT, and GPx were decreased. The 16S rRNA gene sequencing results showed that PFHxA significantly reduced the abundance and diversity of the gut microbiota. It is suggested that PFHxA is likely to cause different degrees of damage to various tissues by disrupting the diversity of the intestinal flora. These results provide insights to facilitate the risk assessment of PFHxA contaminants in the aquatic environment. [Display omitted] • Perfluorocaproic acid can cause damage to immune organs and intestinal tract. • Perfluorocaproic acid can disrupt the intestinal mucosal barrier. • Perfluorocaproic acid can reduce beneficial bacteria in the intestinal tract. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the impact of microplastics (MPs) on fish and to confirm the toxic effects of MPs on fish, as well as to clarify the standard indicators. MPs are present in a large amount in the aquatic environment and can have various adverse effects on aquatic animals. Crucian carp, Carassius carassius (mean weight, 23.7 ± 1.6 g; mean length, 13.9 ± 1.4 cm), were exposed to PA (Polyamide) concentrations of 0, 4, 8, 16, 32 and 64 mg/L for 2 weeks. The PA accumulation profile in C. carassius decreased from the intestine to the gill to the liver. Hematological parameters such as red blood cell (RBC) counts, hemoglobin (Hb), and hematocrit (Ht) notably decreased at high levels of PA exposure. Plasma components such as calcium, magnesium, glucose, cholesterol, total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) were significantly altered by PA exposure. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and glutathione (GSH) of liver, gill and intestine significantly increased following PA exposure. The results of this study suggest that MP exposure affects the hematological physiology and antioxidant responses in C. carassius as well as accumulation in specific tissues. [Display omitted] • Carassius carassius fish were exposed to microplastics (MPs). • The order of accumulation after MP exposure was intestine > gill > liver. • MP exposure at high levels was toxic to C. Carassius. • MPs affect specific tissues, hematological parameters, and antioxidative responses. [ABSTRACT FROM AUTHOR]

Certain bacterial strains could efficiently improve the conversion of insoluble phosphorus to active phosphorus due to their phosphate-solubilizing ability, but there is little research on its specific effects on aquaculture. In this study, a mutant strain Bacillus cereus S458-M was obtained via compound mutagenesis of UV and LiCl. We found it exhibited higher phosphate-solubilizing ability and phytase activity than the original strain S458-1 reported in our previous report. The sequence analysis of phytase gene (phyC) in S458-M revealed mutations in amino acids 81, 89 and 148. Its predicted protein contained an additional Ca2+ binding site that might be associated with higher phytase activity. To verify phosphate-solubilizing and probiotic properties of S458-M, no bacteria (CG: control group), S458-1 (LS: 1 × 105 CFU/mL; HS: 1 × 107 CFU/mL) and S458-M (LM: 1 × 105 CFU/mL; HM: 1 × 107 CFU/mL) were supplemented into aquaculture water separately. The results showed that S458-M could improve the concentration of active phosphorus in aquaculture water and enhance the antioxidant ability of crucian carp. Overall, S458-M obtained by UV-LiCl mutagenesis could support the application of phosphate-solubilizing bacteria in aquaculture water. • UV-LiCl mutagenesis was used in the genetic mutation of Bacillus cereus S458-M. • S458-M exhibited higher phosphate-solubilizing ability and phytase activity. • An additional Ca2+ binding site was observed in the predicted phytase of S458-M. • S458-M could improve the concentration of active phosphorus in aquaculture water. • S458-M could enhance the antioxidant ability of crucian carp. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the toxic effects of polyethylene microplastics (PE-MPs) by measuring the bioaccumulation, hematological parameters, and antioxidant responses in crucian carp (Carassius Carassius) exposed to waterborne 22–71 μm PE-MPs. C. carassius (mean weight, 24.0 ± 2.1 g; mean length, 13.1 ± 1.2 cm) were exposed to PE-MPs at concentration of 0, 4, 8, 16, 32, and 64 mg/L for 2 weeks. The accumulation of PE-MPs in each tissue of C. carassius was significantly increased in proportion to the PE-MPs concentration; the highest accumulation was observed in the intestine, followed by the gills and liver. Hematological parameters, plasma components and antioxidants responses were significantly affected by PE-MPs in a concentration-dependent manner. Exposure to ≥32 mg/L PE-MPs induced a significant decrease in red blood cells (RBCs), hemoglobin (Hb) content, and hematocrit values. However, exposure to ≥32 mg/L PE-MPs induced oxidative stress in the liver, gill, and intestine of C. carassius , thereby resulting in a significant increase in the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) and a decrease in glutathione (GSH) levels. The effects of interaction between the PE-MPs and exposure periods showed no significant changes in bioaccumulation, hematological parameters, plasma components and antioxidant responses. These finding indicate that the exposure to ≥32 mg/L PE-MPs could cause a significant accumulation in specific tissues of C. carassius , resulting in changes in hematological parameters, plasma components, and antioxidant responses. However, the interaction between PE-MPs and exposure periods had no significant effects, thereby suggesting the lack of toxicological interactions between PE-MPs and exposure periods in C. carassius. [Display omitted] • Accumulation pattern of PE-MPs in C. carassius followed the order intestine > gill > liver. • Hematological parameters and plasma components of C. carassius were significantly altered. • PE-MP exposure above 32 mg/L induced significant changes in antioxidant responses of C. carassius. • PE-MP exposure causes blood toxicity and oxidative stress. • Interactive effects between PE-MPs and exposure periods had no significant effects. [ABSTRACT FROM AUTHOR]

A 70-day feeding trial was conducted to investigate the effects of dietary supplementation with prebiotics β-glucan (BG group) and probiotics Bacillus subtilis (BS group) on growth performance, fillet quality, immune response, and antioxidant status of Pengze crucian carp (Carassius auratus var. Pengze). The results showed that supplementation of B. subtilis significantly improved the growth performance than other groups whereas feed efficiency was unaffected by dietary treatments. The textures of muscle in terms of hardness, springiness, cohesiveness, gumminess, chewiness, and resilience were higher in BG and BS groups than Control group. Supplementation of β-glucan and B. subtilis acted as an hypolipidemic in terms of decreasing the total cholesterol, high-density lipoprotein, and low-density lipoprotein whereas, increased the immune responses in serum measured by acid phosphatase, alkaline phosphatase, and catalase activities. Dietary supplementation of β-glucan and B. subtilis significantly improved the fold height and microvillus height in contrast to basal diet. Moreover, β-glucan could significantly increase digestive capacity observed in terms of an increase in amylase and trypsase activities, and B. subtilis significantly increased amylase and lipase activities in intestine. β-glucan and B. subtilis supplementation enhanced the immunity and antioxidant capacity via an increase in acid phosphatase, alkaline phosphatase, glutathione peroxidase, reduce glutathione, catalase, and total superoxide dismutase activities, accompanied by a significant reduction in malondialdehyde. Overall, the results indicated that B. subtilis improved the growth performance by increasing the digestive enzymes activities and improving the intestinal morphology. β-glucan and B. subtilis supplementation significantly improved the fillet quality, immune responses and antioxidant status of Pengze crucian carp. • Dietary supplementation with Bacillus subtilis significantly improved the growth of Pengze crucian carp. • β-Glucan and B. subtilis supplementation significantly affected the fillet quality. • β-Glucan and B. subtilis supplementation significantly improved the immune responses and antioxidant status of fish. [ABSTRACT FROM AUTHOR]

• Biochemical responses of two fish species from two Greek lakes were investigated. • Fish species showed different susceptibility depending on the studied parameters. • Insights into the mechanisms for species acclimation to stressful environments. • The battery of studied biomarkers serves as a tool for lake biomonitoring. Lacustrine ecosystems have been altered by accelerating pollution, excessive nutrient and organic load, water abstraction, and are susceptible to climate change. Hence, suggesting sensitive and reliable biomarkers for early assessments of their status is of urgent need. In this study, two freshwater commercial fish species, Cyprinus carpio (carp) and Carassius gibelio (prussian carp) from two lakes (i.e. Koronia and Volvi, Northern Greece) with different anthropogenic pressures were used and a battery of biochemical and molecular biomarkers related to stress response were analyzed in fish gills and liver. In parallel, water physicochemical parameters (T, DO, pH, conductivity, salinity), BOD 5 and nutrient (N-NO 3 , N-NO 2 , N-NH 4 , P-PO 4) concentrations were measured. Results showed that Lake Koronia had higher conductivity and salinity values and N-NO 2 concentrations. Levels of Heat Shock Response (HSR), MAPK phosphorylation, protein carbonylation, lipid peroxidation products, Bax/Bcl-2 ratio, ubiquitination and caspases were increased in gills and liver of both fish species sampled from Lake Koronia in relation to those of Lake Volvi. Likewise, liver lipid content was increased in both fish species sampled from Lake Koronia compared to those sampled from Lake Volvi. The results indicate and reflect the higher environmental degradation that prevails in Lake Koronia ecosystem in comparison to that of Lake Volvi. The fish species studied showed different susceptibility depending on the biomarkers examined. In addition, our results from both examined species provide insight into the mechanisms involved in acclimatization to stressful environments and support the role of the studied biomarkers as sensitive and reliable tools for ecological assessments of lake ecosystems in biomonitoring studies. [ABSTRACT FROM AUTHOR]

Information on biomagnification of alternative brominated flame retardants (ABFRs) is limited and results are inconclusive, due in part to uncertainty in the understanding of predator/prey relationships. In the present study, a predatory fish, Channa argus , and several forage fish species were obtained from an ABFR contaminated site. The predator/prey relationships were identified based on fatty acid (FA) signatures in the predator and prey. Biomagnification factors (BMFs) for several ABFRs including decabromodiphenyl ethane (DBDPE), 1,2‑bis(2,4,6‑tribromophenoxy) ethane (BTBPE), hexabromobenzene (HBB), pentabromotoluene (PBT), and pentabromoethylbenzene (PBEB) were estimated based on the identified predator/prey relationships. The results showed that crucian carp was the main prey of C. argus , contributing to 71%–100% to its total diet. The mean BMFs for DBDPE, BTBPE, and HBB were 0.06, 0.40, and 0.91, respectively, indicating trophic dilution of these ABFRs. However, biomagnification of PBT and PBEB, with BMFs of 2.09 and 2.13, respectively, was observed. The BMFs for PBT, PBEB and HBB were comparable to or even higher than those for some polybrominated diphenyl ether (PBDE) congeners estimated in the same individual predator, indicating that these emerging pollutants may pose significant environmental risks. The BMFs for ABFRs and PBDEs were significantly and negatively correlated to the log K OW s of these chemicals, suggesting that the biomagnification of these chemicals was depressed due to their superhydrophobic nature. • BMFs for ABFRs were estimated based on diet composition of the predator. • PBT and PBEB magnified while DBDPE, BTBPE, and HBB diluted in the predator. • BMFs for ABFRs are comparable to or even higher than those for PBDEs. • One of the few reports on the biomagnification potential of ABFRs. [ABSTRACT FROM AUTHOR]

Abstract The occurrence and distribution of 41 congeners of polychlorinated naphthalenes (PCNs) were investigated in major tissues of crucian carp (muscle, gonad, liver, and blood) and in river sediment to assess the bioaccumulation potential of PCNs. The total PCN concentrations in sediment ranged from 4.37 to 19.5 pg/g dry weight (dw), mainly comprising CN-13, CN-33/34/37, and CN-38/40. Among fish tissues, higher PCN concentrations were observed in the gonads (29.6 ± 10.3 pg/g wet weight, ww) and liver (25.7 ± 4.35 pg/g ww) of crucian carp than in the muscle (2.17 ± 0.68 pg/g ww). CN-28/43, CN-33/34/37, CN-42, CN-52/60, CN-53/55, and CN-66/67 congeners were detected most frequently and had the highest concentration among all crucian carp tissues. We investigated the association between the PCN concentration in each tissue (muscle, liver, and gonad) and the size of the fish (total length and weight) and found positive correlations between the PCN concentration in the gonads and the total length and weight (p < 0.05, Spearman correlation). Graphical abstract Unlabelled Image Highlights • The level and distribution of PCNs were investigated in sediment and fish. • The PCNs accumulation in sediment was mainly influenced by combustion and Halowax. • The congeners with PCN-NVC and PCN-DVC structures had high levels in fish tissues. • PCNs levels in gonad tissue of crucian carp increased as crucian carp grew. [ABSTRACT FROM AUTHOR]

Abstract Animals adapt to the challenges of fluctuations in predator risk and food availability in their natural habitats. Phenotypic plasticity allows animals to handle environmental changes. However, the patterns of flexibility in metabolic rates and its ecological consequences under different predator stress and food availability conditions are poorly understood. Here, we used crucial carp (Carassius auratus) as a prey species and northern snakehead (Channa argus) as a predator to test whether predator stress influences metabolism and growth, and alters the link between flexibility in metabolic rate and its ecological consequences (e.g., growth) in crucial carp. The experiment was carried out under the conditions of predator stress (with or without a predator) and three food availabilities (satiation feeding 1 time per day, low food availability; 2 times per day, intermediate food availability; and 3 times per day, high food availability) for 3 weeks. After 21 days of feeding, the final body mass and body length in the two treatments increased compared to the initial values in all three food availabilities. The feeding intake (FI) and specific growth rate (SGR) of the two treatments increased with increasing food availability. The control treatment had a higher FI and SGR than the predator stress treatment in all three food availabilities. The feeding efficiency (FE) of the two treatments was higher at the high and intermediate food availabilities than at the low food availability. However, no effect of predator stress on FE was detected. The final values of original or standardized SMR were higher in the control treatment than the predator stress treatment at the intermediate and high food availabilities. The changes in SMR (ΔSMR) were higher in the control treatment than in the predator stress treatment. The positive correlation between the ΔSMR and SGR was found in the intermediate food availability in the predator stress treatment, suggesting that individuals with a higher flexibility in SMR had a larger growth rate and vice versa, but this relationship was dependent on food availability. Our results suggest that predator stress decreased maintenance metabolism, feeding and growth of juvenile crucial carp irrespective of food availability. Predator stress does not alter the growth advantages conferred by the metabolic plasticity of the fish under changing food availability. Highlights • The morphology, feeding intake and specific growth rate of the two predator stress treatments increased with increasing food availability. • The changes in standard metabolic rate were higher in the control treatment than in the predator stress treatment at the intermediate food availability. • Predator stress does not alter the correlations between the changes in standard metabolic rate and growth. [ABSTRACT FROM AUTHOR]