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Grass carp was an important economic fish for freshwater aquaculture. The exploring and utilization of high-quality grass carp germplasm resources were important for ensuring a domestic supply of high-quality aquatic protein. However, natural grass carp populations in China were facing severe threats because of the effects of frequent human activities, water environment damage, overfishing, etc. Against this background, high-quality grass carp germplasm resources were the foundation for the healthy and sustainable development of the grass carp aquaculture industry, so systematic collection, preservation, identification, evaluation, protection, and utilization of them carry great strategic importance. This paper summarizes major research results of grass carp in morphology, cytogenetics, molecular population genetics, etc. It not only introduced genetic improvement techniques such as gynogenesis, hybrid breeding, and polyploid breeding, but also discussed the existing research on the protection measures of grass carp germplasm resources. On this basis, the paper proposed new methods to improve the protection of grass carp germplasm and create improved varieties, which could provide high-quality resources for the sustainable development of the grass carp industry. [ABSTRACT FROM AUTHOR]

To maintain the health of aquaculture fish, it is critical to understand the composition of microorganisms in aquaculture water and sediment and the factors affecting them. This study examined the water and sediment microbiota compositions of four different types of ponds in South China that were used to culture grass carp (Ctenopharyngodon idella) of different sizes through high-throughput sequencing of the 16S rRNA gene, and analyzed their correlations with environmental factors. The results showed that ponds with cultured grass carp of different sizes exhibited significant differences in terms of water physicochemical properties and composition of water and sediment microbiota. Furthermore, the exchange of microorganisms between water and sediment microbiota was lowest in ponds with the smallest grass carp and highest in ponds with the largest grass carp. All detected environmental factors except water temperature were significantly correlated with the water microbiota, and all detected environmental factors in the sediment were correlated with sediment microbiota. Moreover, Aeromonas hydrophila and Vibrio were significantly increased in the water microbiota, especially in ponds with small juvenile grass carp, implying an increased risk of A. hydrophila and Vibrio infections in these environments. Our results provide useful information for the management of grass carp aquaculture ponds. [ABSTRACT FROM AUTHOR]

In‐pond raceway systems (IPRS) are a high‐density ecological green pond aquaculture mode, which has developed rapidly in China in recent years. This study evaluated the flesh quality and physiological response of grass carp under the IPRS mode. Compared with the traditional earthen pond (EP) mode, the grass carp hepatosomatic index and viscerosomatic index under the IPRS mode are significantly (p < 0.05) lower. And the water holding capacity of grass carp muscles were significantly (p < 0.05) improved. Compared with EP mode, grass carp muscles under the IPRS mode have more crude protein content and less crude fat content, and have higher muscle fiber density and smaller muscle fiber diameter. In the IPRS mode, the total amount of essential amino acids (∑EAA) in grass carp muscle increased significantly (p < 0.05), and the content of savory amino acids increased significantly (p < 0.05). In addition, the content of eicosapentaenoic acid and docosahexaenoic acid in the muscle fatty acids of IPRS grass carp was also significantly (p < 0.05) higher than EP mode. At the same time, in order to cope with the high‐density culture mode of IPRS, the activity of catalase and superoxide dismutase in grass carp muscle was significantly (p < 0.05) increased, and the alanine aminotransferase in serum, aspartate aminotransferase, as well as other biochemical indexes, increased significantly (p < 0.05). In the IPRS mode, the mass‐specific lamellae respiratory area of the gill increased significantly (p < 0.05), and the volume of the interlaminar cell mass decreased significantly (p < 0.05) to increase oxygen intake. Taken together, our results show that grass carp will produce relevant physiological response to cope with the IPRS high‐density culture environment, while their flesh yield, flesh quality, and nutritional value is improved. [ABSTRACT FROM AUTHOR]

Larvae of black carp (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idella), silver carp (Hypophthalmichthys molitrix), and bighead carp (Hypophthalmichthys nobilis) were collected at a stationary location in the Changsha section of the Xiangjiang River from May, 2011 to July, 2020, and the relationships between abundance of the larvae and hydrological indices were analysed. Our results showed that the first appearance time of the larvae exhibited obvious annual differences, most of which were concentrated in mid-to-late May and early June, whereas 2016 was advanced to early May, which was the earliest year in the investigated 10 years. Moreover, the larval emergence was concentrated in mid-to-late May from 2017 to 2020, which was significantly earlier than those in early June of 2011-2013. Larval compositions of the four major carp species were significantly different between different years. Only water temperature significantly correlated with the compositions of the four major carp larvae. Water temperature significantly correlated with the catch-per-unit-of-effort of C. idella larvae, and rainfall for 3 consecutive days significantly correlated with the catch-per-unit-of-effort of H. nobilis larvae. [ABSTRACT FROM AUTHOR]

Grass carp is an economically important freshwater fish in China, and haemorrhagic disease caused by GCRV has seriously restricted its farming scale. To understand the host molecular basis for antiviral defence and explore the effector molecules, a global transcriptional profiling of four major immune tissues (liver, spleen, head kidney, and trunk kidney) of GCRV-infected grass carp was established. A total of 192.65 Gb clean data was obtained with 6.11 Gb per sample and stored in the NCBI Sequence Read Archive (with accession number PRJNA759556). Based on the GO and KEEG analyses, 108 unique GO terms were enriched in the four tissues. Thirty-five enriched pathways were obtained, with 21 metabolism-related pathways mainly gained in the liver and trunk kidney, and 14 immune response pathways were enriched in the spleen and head kidney. Also demonstrated was that GCRV stimulates not only the expression of interferon-stimulated genes (ISGs) but also proinflammatory cytokines. 27 ISGs were screened from the candidate DEGs, and eight ISGs were identified for the first time in grass crap. These ISGs were classified into three categories by their function found in mammals: (i) positively regulates the IFN signalling pathway (RIG-I, MDA5, IRF7, IRF9, STAT2, and TRIM25); (ii) negatively regulates the IFN signalling pathway (usp18 and SOCS1); and (iii) exerts direct antiviral activity such as Mx1, ISG15, ISG56, ISG58, viperin, and PKR. Eight major ISGs and four typical differentially inflammatory cytokines were used for further expression analysis with prominent expression in the liver, spleen and kidney. The onset time of IFN-mediated antiviral response was trunk kidney (12–24 h) > liver (48 h) > spleen (96–120 h), and the intensity was liver > spleen > trunk kidney. Notably, the inflammatory reaction occurs early in the liver and trunk kidney. This result implies that ISGs may act synergistically and that the IFN response is closely related to the inflammatory response against GCRV infection. The transcriptomic profiles obtained and the function of ISGs predicted in this study provide new insights into fish antiviral mechanisms and developing effective therapeutic directions. • 35 enriched pathways were obtained, with 21 metabolism-related pathways mainly gained in the liver and trunk kidney, and 14 immune response pathways were enriched in the spleen and head kidney. • 27 ISGs were screened which can be classified into three categories (i) positively regulates the IFN signalling pathway (RIG-I, MDA5, IRF7, IRF9, STAT2, and TRIM25); (ii) negatively regulates the IFN signalling pathway (usp18 and SOCS1); and (iii) exerts direct antiviral activity such as Mx1, ISG15, ISG56, ISG58, viperin, and PKR. • The candidated ISGs show a tissue-specific property and may act synergistically, meanwhile, that the IFN response is closely related to the inflammatory response against GCRV infection. [ABSTRACT FROM AUTHOR]

Background: Grass carp are an important farmed fish in China that are infected by many pathogens, especially grass carp reovirus (GCRV). Notably, grass carp showed age-dependent susceptibility to GCRV; that is, grass carp not older than one year were sensitive to GCRV, while those over three years old were resistant to this virus. However, the underlying mechanism remains unclear. Herein, whole genome-wide DNA methylation and gene expression variations between susceptible five-month-old (FMO) and resistant three-year-old (TYO) grass carp were investigated aiming to uncover potential epigenetic mechanisms. Results: Colorimetric quantification revealed that the global methylation level in TYO fish was higher than that in FMO fish. Whole-genome bisulfite sequencing (WGBS) of the two groups revealed 6214 differentially methylated regions (DMRs) and 4052 differentially methylated genes (DMGs), with most DMRs and DMGs showing hypermethylation patterns in TYO fish. Correlation analysis revealed that DNA hypomethylation in promoter regions and DNA hypermethylation in gene body regions were associated with gene expression. Enrichment analysis revealed that promoter hypo-DMGs in TYO fish were significantly enriched in typical immune response pathways, whereas gene body hyper-DMGs in TYO fish were significantly enriched in terms related to RNA transcription, biosynthesis, and energy production. RNA-seq analysis of the corresponding samples indicated that most of the genes in the above terms were upregulated in TYO fish. Moreover, gene function analysis revealed that the two genes involved in energy metabolism displayed antiviral effects. Conclusions: Collectively, these results revealed genome-wide variations in DNA methylation between grass carp of different ages. DNA methylation and gene expression variations in genes involved in immune response, biosynthesis, and energy production may contribute to age-dependent susceptibility to GCRV in grass carp. Our results provide important information for disease-resistant breeding programs for grass carp and may also benefit research on age-dependent diseases in humans. [ABSTRACT FROM AUTHOR]

Bacterial septicemia represents a significant disease affecting cultured grass carp culture, with the primary etiological agent identified as the Gram-negative bacterium Aeromonas veronii. In response to an outbreak of septicemia in Guangzhou, we developed a formaldehyde-inactivated vaccine against an A. veronii strain designated AV-GZ21-2. This strain exhibited high pathogenicity in experimental infections across at all developmental stages of grass carp. Mortality rates for grass carp weighing 15 ± 5 g ranged from 16 % to 92 % at exposure temperatures of 19 °C-34 °C, respectively. The median lethal dose (LD 50 ) for grass carp groups weighing 15 ± 5 g, 60 ± 10 g, 150 ± 30 g and 500 ± 50 g were determined to be 1.43, 2.52, 4.65 and 7.12 × 10 7 (CFU/mL), respectively. We investigated the inactivated vaccine in conbination with aluminum hydroxide gel (AV-AHG), Montanide ISA201VG (AV-201VG), and white oil (AV-WO) adjuvants. This study aimed to optimize inactivation conditions and identify the adjuvant that elicits the most robust immune response. The AV-GZ21-2 inactivated bacterial solution (AV),when combined with various adjuvants, was capable of inducing a strong specific immune response in grass carp. The relative percent survival (RPS) following a lethal challenge with AV-GZ21-2 were 94 % for AV-AHG, 88 % for AV-201VG, 84 % for AV-WO and 78 % for AV alone. The minimum immunization dose of the AV-AHG vaccine was determined to be 6.0 × 10 7  CFU per fish, providing immunity for a duration of six months with an immune protection level exceeding 75 %. Furthermore, the AV-AHG vaccine demonstrated significant protective efficacy against various epidemic isolates of A. veronii. Consequently, we developed an inactivated vaccine targeting a highly pathogenic strain of A. veronii, incorporating an aluminum hydroxide gel adjuvant, which resulted in high immune protection and a duration of immunity exceeding six months. These findings suggest that the AV-AHG vaccine holds substantial potential for industrial application., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in the manuscript entitled “Evaluation of virulence of Aeromonas veronii strain GZ21-2 and development of a highly effective vaccine for grass carp with the potential for industrial application”., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The grass carp Ctenopharyngodon idella is a commercially relevant carp species with a long-term artificial release history in China. To date, several genetic diversity studies have been performed on the Yangtze River C. idella populations, but similar reports were sparse for the Pearl River populations. Here, our study explored the genetic diversity patterns and population structure of the Pearl River C. idella populations after human intervention using two mitochondrial loci. Phylogenetic analyses demonstrated that grass carp populations in the Pearl River exhibited two maternal genetic lineages. Haplotype networks demonstrated that most main Pearl River haplotypes were shared with those of the Yangtze River samples. No genetic structure was detected among the Pearl populations and low level of population differentiation was observed between individual Yangtze River populations and the Pearl River populations. These findings might be attributed to the high dispersal ability of grass carp, as well as anthropogenic release. Moreover, the nucleotide diversity of the Pearl River populations was higher than that of the Yangtze River, indicating that artificial release programs might have significant effects on the genetic diversity of the Pearl River populations. Taken together, our findings demonstrated artificial release programs may have influenced the Pearl River grass carp populations and provide important knowledge that may guide the future management of grass carp in the Pearl River. [ABSTRACT FROM AUTHOR]

Grass carp (Ctenopharyngodon idella) is a widely cultivated freshwater fish in the world, which occupies a leading position in China's aquaculture industry. However, the outbreak of hemorrhagic disease resulted from grass carp reovirus (GCRV) infection causes tremendous loss in grass carp production. In this study, we cloned the cDNA of grass carp SIRT3 (gc-SIRT3) and found that it is highly conserved across species and abundantly expressed in grass carp liver. Upon GCRV infection, the expression of gc-SIRT3 is dynamically changed. In addition, grass carp SIRT3 positively regulates the expression of antiviral genes depending on its enzymatic activity. Mechanistically, gc-SIRT3 interacts with gc-MAVS to enhance the MAVS-mediated antiviral response. Furthermore, SIRT3 inhibition in zebrafish or grass carp larvae with the specific inhibitor, 3-TYP, attenuates the antiviral ability against GCRV infection. Our findings may provide clues for understanding the function of SIRT3 in antiviral innate immunity. • Grass carp SIRT3 expression is dynamically changed upon GCRV infection. • Grass carp SIRT3 enhances antiviral gene expression depending on its enzymatic activity. • Grass carp SIRT3 interacts with MAVS to enhance the MAVS-mediated antiviral response. • SIRT3 inhibition with 3-TYP attenuates the antiviral ability against GCRV infection. [ABSTRACT FROM AUTHOR]

Grass carp (Ctenopharyngodon idellus) is an important aquaculture species in China that is affected by serious diseases, especially hemorrhagic disease caused by grass carp reovirus (GCRV). Grass carp have previously shown age-dependent susceptibility to GCRV, however, the mechanism by which this occurs remains poorly understood. Therefore, we performed transcriptome and metabolome sequencing on five-month-old (FMO) and three-year-old (TYO) grass carp to identify the potential mechanism. Viral challenge experiments showed that FMO fish were susceptible, whereas TYO fish were resistant to GCRV. RNA-seq showed that the genes involved in immune response, antigen presentation, and phagocytosis were significantly upregulated in TYO fish before the GCRV infection and at the early stage of infection. Metabolome sequencing showed that most metabolites were upregulated in TYO fish and downregulated in FMO fish after virus infection. Intragroup analysis showed that arachidonic acid metabolism was the most significantly upregulated pathway in TYO fish, whereas choline metabolism in cancer and glycerophospholispid metabolism were significantly downregulated in FMO fish after virus infection. Intergroup comparison revealed that metabolites from carbohydrate, amino acid, glycerophospholipid, and nucleotide metabolism were upregulated in TYO fish when compared with FMO fish. Moreover, the significantly differentially expressed metabolites showed antiviral effects both in vivo and in vitro. Based on these results, we concluded that the immune system and host biosynthesis and metabolism, can explain the age-dependent viral susceptibility in grass carp. [ABSTRACT FROM AUTHOR]

The gut microbiota is closely related to health and disease. Grass carp (Ctenopharyngodon idella) is an important food fish in China. We aimed to investigate the effect of a chicken faeces diet on the gut microbiota composition of grass carp reared in an integrated farming system in China. Gut microbiota compositions of grass carps fed chicken faeces, a commercial diet, and grass were compared based on 16S rRNA gene sequencing. The major intestinal phyla in grass carps fed chicken faeces were Firmicutes, Proteobacteria, and Actinobacteria. The untreated chicken faeces diet altered the gut microbiota composition and increased the number of potential pathogens and antibiotic-resistant bacteria in the gut to varying degrees. To reduce the risk of diseases, it is necessary to remove residual antibiotics and antibiotic-resistant bacteria in chicken faeces by fermentation or other techniques, before it can be used as a fish feed for grass carp. [ABSTRACT FROM AUTHOR]

• Grass carp MBSP's role in surimi deterioration was examined for the first time. • Crude MBSP reduced surimi quality significantly after increasing the original content by 30%. • In the "modori" effect, the myosin head may be the primary region of degradation. Grass carp (Ctenopharyngodon idella) are used as raw material for conventional surimi products in Southern China. However, endogenous serine proteases deteriorated the texture of the surimi gel. To unlock the mechanism behind, the present study isolated the crude myofibril-bound serine protease (cMBSP) in grass carp and studied its effects on surimi gel. The cMBSP activity was the highest at 40 °C and pH 8.0, and it remained stable at 20–55 °C neutral pH. Additionally, it was susceptible to serine protease inhibitors and high concentrations of Na+. The maximum degradation of myosin heavy chain by cMBSP was observed at 50 °C. Protein unc-45 homolog B (a myosin chaperone) is one of the apparent degradation products according to mass spectrometry. The cMBSP caused lower water holding capacity and deteriorated texture in the surimi gel. This study expanded insights about the mechanism of surimi gel degradation by cMBSP, which provided theoretical basis for enhancing surimi quality. [ABSTRACT FROM AUTHOR]

Grass carp (Ctenopharyngodon idellus) is one of the most important aquaculture fish in China. This study tried to explore the effects of dietary alcoholic extract of lotus leaf (AELL) addition on the growth performance and health status of grass carp by feeding juvenile fish (average weight: 34 ± 1 g) with four different experimental diets: control, AELL7, AELL14 and AELL21 for 8 weeks. At the end of the growth trial, the highest values of final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR) and feed intake (FI) all occurred in group AELL14 (P < 0.05). Compared to control, the crude lipid content of whole-body and the serum malondialdehyde (MDA) in the three experimental groups decreased, while the serum superoxide dismutase (SOD), glutathione peroxidase (GSH) and total antioxidant capacity (T-AOC) values almost all increased in the three experimental groups. The highest serum immunoglobulin M (IgM) concentration occurred in AELL14 group (P < 0.05). In AELL14 and AELL21 groups, both the serum complement 3 (C3) concentration and lysozyme (LYS) activity were significantly higher, whereas the final cumulative mortality in challenge test was significantly lower, when compared to those in control group (P < 0.05). The AELL exerted dose-dependent beneficial effects on grass carp health through up-regulating related gene expressions and enzyme activity. In conclusion, the optimal dietary AELL level is 0.14% for juvenile grass carp. • Lotus leaf extract can improve growth performance and health status of grass carp. • Lotus leaf extract exhibited dose-dependent beneficial effects on grass carp. • Optimal lotus leaf extract inclusion level in the grass carp diet is 0.14%. [ABSTRACT FROM AUTHOR]

Grass carp ( Ctenopharyngodon idellus ) is an economical aquaculture species in China, and the Grass Carp Reovirus (GCRV) that causes hemorrhagic disease seriously affects the grass carp cultivation industry. Substantial evidence indicates that there is an association between the membrane-associated RING-CH family of E3 ligase (MARCH) family and immune defense in mammals, while functional studies on non-mammalian MARCH proteins are limited. In order to know the characteristics of the MARCH genes in C. idellus , eight MARCH genes ( MARCH1, 2, 5, 6, 7, 8, 9 and 11 ) were cloned and the open reading frames (ORF) were identified in grass carp. All MARCH proteins in grass carp contained an RING-CH domain, which is characteristic of the MARCH protein. The phylogenetic analysis revealed that different MARCH proteins gathered into their separate clusters. All eight members of the MARCH gene family were detected in all tissues sampled, but the relative expression level differed. In addition, the mRNA expression of all the MARCHs was regulated at different levels in the immune organs after a GCRV challenge, and they responded robustly in both the intestine and liver. The mRNA expression of MARCH8, MHC II, TfR, IL1RAP, EGR1, and DUSP1 in the intestine after GCRV infection was analyzed, and the results showed that MARCH8 could negatively regulate TfR, IL1RAP, EGR1, and DUSP1, which signaled via the MAPK or NF-κB-activation pathways that play vital roles in immunity. Our findings identified a novel gene family in C. idellus and provided novel evidence that MARCH genes are inducible and involved in the immune response. Moreover, MARCH8 might function to negatively regulate immune receptors in C. idellus . Therefore, the MARCH might play a vital role in regulating the immune response of C. idellus . [ABSTRACT FROM AUTHOR]

Grass carp (C. idella) is an important farmed freshwater fish in China. In recent years, grass carp hemorrhagic diseases caused by viruses, bacteria, and parasites have hindered the aquaculture industry; however, there are few studies on the hematopoiesis of grass carp. It is reported that erythropoiesis is a complex biological process, which requires hematopoietic-stimulating factors, inhibitors, the hematopoietic microenvironment, and stromal cells to interact for fine regulation. In this study, ischemic anemia (a blood loss model) and hemolytic anemia (a hemolysis model) were established to stimulate hematopoiesis of grass carp. The hematopoietic organs of grass carp were studied using tissue imprinting, hematoxylin-eosin (H&E) staining, western blot (WB), and immunofluorescence assay (IFA). Hematopoietic-stimulating factors and iron metabolism-related factors were detected by quantitative real-time PCR (qRT-PCR). The results of tissue imprinting showed that there were proerythrocytes in the head kidney, spleen, and middle kidney. In the model of ischemic anemia, a hematopoietic island could be found in head kidney and spleen at 24 h. The hematopoietic island appeared in the middle kidney on the 7th day. The results of H&E staining showed that when the peripheral blood decreased sharply, the spleen compensated for the peripheral blood and decreased the melanin macrophage center in head kidney, spleen, and middle kidney. The results of WB, IFA, and qRT-PCR showed that the hematopoietic pathway and iron metabolism were activated in both models. In sum, the head kidney, spleen, and middle kidney of grass carp are its main hematopoietic organs, and the head kidney is the most important. The spleen is an important blood bank of grass carp and hematopoiesis compensation occurs in the spleen and mesonephros during severe ischemia. • The head kidney, spleen, and middle kidney are main hematopoietic organs in grass carp. • Ischemic anemia activated the expression of hematopoietic-stimulating factors genes. • Ischemic anemia modulated the expression of iron metabolism-related genes. • PHZ-induced modulated the expression of hematopoietic-associated and iron metabolism-related genes. [ABSTRACT FROM AUTHOR]

To maintain the health of aquaculture fish, it is critical to understand the composition of microorganisms in aquaculture water and sediment and the factors affecting them. This study examined the water and sediment microbiota compositions of four different types of ponds in South China that were used to culture grass carp ( Ctenopharyngodon idella ) of different sizes through high-throughput sequencing of the 16S rRNA gene, and analyzed their correlations with environmental factors. The results showed that ponds with cultured grass carp of different sizes exhibited significant differences in terms of water physicochemical properties and composition of water and sediment microbiota. Furthermore, the exchange of microorganisms between water and sediment microbiota was lowest in ponds with the smallest grass carp and highest in ponds with the largest grass carp. All detected environmental factors except water temperature were significantly correlated with the water microbiota, and all detected environmental factors in the sediment were correlated with sediment microbiota. Moreover, Aeromonas hydrophila and Vibrio were significantly increased in the water microbiota, especially in ponds with small juvenile grass carp, implying an increased risk of A. hydrophila and Vibrio infections in these environments. Our results provide useful information for the management of grass carp aquaculture ponds., Competing Interests: Yingli Lian, Jian Wang, Jiayi Tang, Xuan Zhu and Baojun Shi are employed by Guangdong Haid Group Co., Ltd. Sampling was conducted at a site associated with Guangzhou Chengyi Aquatic Technology Co., Ltd., China, which is partner to one of our affiliations., (©2023 Lian et al.)

• Grass carp could adapt to low salinity (2 ppt). • Grass carp maintained a stable physiological and immune status at low salinity. • Salinity altered the microbial composition in the gut of the grass carp. • High salinity induced a decrease in the proportion of probiotics and an increase in the proportion of harmful bacteria in the gut. Grass carp (Ctenopharyngodon idella) is among the most important freshwater fish species in China. However, it remained unclear how salinity could affect grass carp. Two experiments were performed. The first experiment was a 4-day acute salt tolerance experiment with six salinities (0, 4, 8, 12, 16, and 20 ppt). The second experiment was an 8-week chronic salt stress experiment with three salinities (0, 2 and 6 ppt). To investigate the intestinal bacterial community of grass carp from three salinities (0, 2, and 6 ppt), the 16S rDNA sequencing was performed. The results showed that grass carp exhibited great adaptability to low salinity (2 ppt), with no significant difference in growth and maintained stable physiological and immune status. However, exposed to high salinity (6 ppt) caused significant deleterious effects on grass carp, including growth inhibition as well as physiological and immune-related changes. The gut microbiota in grass carp changed with salinity. With the increase of salinity, the proportion of beneficial bacteria in the gut of grass carp gradually decreased, while some harmful bacteria gradually occupied the dominant position. Changes in gut microbial composition ultimately affected the growth of grass carp. This study helps further clarify the effects of salinity on grass carp. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the nutrient dynamics and balance of zero–water exchange ponds of grass carp Ctenopharyngodon idella , crucian carp Carassius auratus and bighead carp Aristichthys nobilis , and explain advantages of the zero–water exchange mode from the perspective of material flow. This study was conducted for two years. The polyculture ponds of grass carp, crucian carp and bighead carp were grouped into the treatment group using the zero–water exchange mode, while the ordinary polyculture ponds of grass carp, bighead carp, and crucian carp were grouped into the control group. The results showed that 1) the treatment group reduced water conductivity, dissolved solids and sediment organic carbon significantly (P < 0.05), and improved water transparency significantly (P < 0.05); 2) the carbon, nitrogen, and phosphorus accumulation amount and rate in the water of the treatment group were significantly lower (P < 0.05) than those in the control group, so was the sediment accumulation rate of organic carbon and nitrogen (P < 0.05); 3) the carbon, nitrogen, and phosphorus utilization efficiency of stocked fish in the treatment group were significantly higher (P < 0.05) than those in the control group, with an increase of 29.49%, 21.72%, and 20.65%, respectively. Therefore, the zero–water exchange pond was a green and efficient aquaculture mode, which could improve water quality, reduce nutrient accumulation, and improve the utilization efficiency of nutrients effectively. Considering the nutrient emissions from aquaculture in China, the zero–water exchange mode has a good value for promotion. • The zero-water exchange ponds reduced the water and sediment accumulation rate. • The zero-water exchange ponds reduced the sediment accumulation rate of organic carbon and nitrogen significantly by 48.98% and 13.97%, respectively. • Utilization efficiency of organic carbon, nitrogen and phosphorus in the zero-water exchange ponds were improved. [ABSTRACT FROM AUTHOR]

The grass carp, which is one of the most important farmed fish species in China, is widely distributed in different river basins. In this study, 21 single nucleotide polymorphism markers, developed in the grass carp expressed sequence tag database, were used with the snapshot genotyping method to analyze the genetic structure of six grass carp populations (SS, JL, HH, YJ, NX, and FS) from the Yangtze River and the Pearl River. The effective numbers of alleles ( Ne) of the six grass carp populations was 1.7680-1.8038, the observed heterozygosity ( Ho) was 0.5938-0.6305, the expected heterozygosity ( He) was 0.4420-0.4443, and the polymorphic information content ( PIC) was 0.3241-0.3403. The PIC, Ne, and He of the JL population were the highest among all populations, whereas those of the YJ population were the lowest. The NJ tree analysis based on genetic distance of the grass carp populations revealed that the six populations clustered into two branches: the SS, JL, and HH populations clustered first into one branch, which then clustered with YJ population; the FS and NX populations constituted a separate branch. The established genetic structures and phylogenetic relationships of some of the grass carp populations of the Yangtze River and Pearl River may lay the foundation for selecting core breeding populations. [ABSTRACT FROM AUTHOR]

Grass carp ( Ctenopharyngodon idella) is a valuable aquacultural species in China, but it is highly vulnerable to infectious diseases, which consequently may cause tremendous economical loss. To reduce the risk of disease in the fish, antibiotics have been used in the fish diet, which in turn caused some negative effects on human health. In this study, we choose lactosucrose ( LS) as antibiotic alternative added to the diet of the grass carp juveniles and then to evaluate the effects of 15 g Kg−1 LS in the diet on the gene transcript profiles. After the trial for 56 days, we observed that the weight gain rate, specific gain rate and feed conversion rate were increased by 14.2%, 9.2% and 10.1%, respectively, in the trial group compared with the control group. The gene expression levels in the liver tissues of grass carps were assayed using the zebrafish c DNA microarray technology and real-time RT- PCR. Comparing with the control group, 416 genes were identified, and among them, 266 genes were up-regulated and 150 were down-regulated on the trial group. Among the up-regulated genes selected, most of them related to growth, immune reaction and sugar metabolism. Most of the down-regulated genes are RAS oncogene family members, V-myc viral oncogene homologue and programmed cell death-related factors. The apparent regulation of gene expression stimulated by LS suggests that the potential application of the LS in improving the growth performance and immunity on the grass carps. Together, this study provides convincing data in support of the use of LS as an alternative dietary antibiotic in fish. [ABSTRACT FROM AUTHOR]

Abstract: A reovirus was isolated from sick grass carp in Guangdong, China in 2009, and tentatively named ‘grass carp reovirus Guangdong 108 strain’ (GCRV-GD108). This reovirus was propagated in grass carp snout fibroblast cell line PSF with no obvious cytopathic effects. Its genome was 24,703bp in length with a 50% G+C content and 11 dsRNA segments encoding 11 proteins instead of 12 proteins. It has been classified as an Aquareovirus (AQRV). Sequence comparisons showed that it possessed only 7 homologous proteins to grass carp reovirus (GCRV) (with 17.6–45.8% identities), but 9 homologous proteins to mammalian orthoreoviruses (MRV) (with 15–46% identities). GCRV-GD108 lacked homology to VP7, NS4&NS5 and NS3 of GCRV, while it had sigma1 and sigma NS homology to MRV. VP2 of GCRV-GD108 shared high amino acid sequence identity (44–47%) with AQRVs, whereas VP5 did not exhibit much identity (24–25%) to AQRVs. Conserved terminal sequences, 5′-GUAAUUU and UUCAUC-3′, were found in all of the 11 genomic segments of GCRV-GD108 at the 5′ and 3′ non-coding regions (NCRs) of the segments. The 5′ NCRs of GCRV-GD108 was similar to GCRV, but differed from other species of AQRV or Orthoreoviruses (ORV). Phylogenetic analysis of coat proteins belonging to Reoviridae, VP1–VP6, showed that GCRV-GD108 clustered with AQRVs and grouped with ORVs, suggesting that GCRV-GD108 belonged to the genus Aquareovirus but was distinctive from any known species of AQRV. Morphological and pathological analyses, and genetic characterization of GCRV-GD108 suggested that it may be a new species of AQRV and it was more closely related with ORVs than other AQRVs. In addition, RT-PCR analysis of diseased grass carp samples collected from different regions of China indicated that these viruses displayed high similarities to each other (95.3–99.4%). They also shared high sequence similarities to GCRV-GD108 (96.7–99.4%), indicating that GCRV-GD108 is representative of the prevalence strain in southern China. [Copyright &y& Elsevier]

Background: A virus was isolated from diseased turbot Scophthalmus maximus in China. Biophysical and biochemical assays, electron microscopy, and genome electrophoresis revealed that the virus belonged to the genus Aquareovirus, and was named Scophthalmus maximus reovirus (SMReV). To the best of our knowledge, no complete sequence of an aquareovirus from marine fish has been determined. Therefore, the complete characterization and analysis of the genome of this novel aquareovirus will facilitate further understanding of the taxonomic distribution of aquareovirus species and the molecular mechanism of its pathogenesis. Results: The full-length genome sequences of SMReV were determined. It comprises eleven dsRNA segments covering 24,042 base pairs and has the largest S4 genome segment in the sequenced aquareoviruses. Sequence analysis showed that all of the segments contained six conserved nucleotides at the 5' end and five conserved nucleotides at the 3' end (5'-GUUUUA ---- UCAUC-3'). The encoded amino acid sequences share the highest sequence identities with the respective proteins of aquareoviruses in species group Aquareovirus A. Phylogenetic analysis based on the major outer capsid protein VP7 and RNA-dependent RNA polymerase were performed. Members in Aquareovirus were clustered in two groups, one from fresh water fish and the other from marine fish. Furthermore, a fusion associated small transmembrane (FAST) protein NS22, which is translated from a non-AUG start site, was identified in the S7 segment. Conclusions: This study has provided the complete genome sequence of a novel isolated aquareovirus from marine fish. Amino acids comparison and phylogenetic analysis suggested that SMReV was a new aquareovirus in the species group Aquareovirus A. Phylogenetic analysis among aquareoviruses revealed that VP7 could be used as a reference to divide the aquareovirus from hosts in fresh water or marine. In addition, a FAST protein with a non-AUG start site was identified, which partially contributed to the cytopathic effect caused by the virus infection. These results provide new insights into the virus-host and virus-environment interactions. [ABSTRACT FROM AUTHOR]

Abstract: Citrobacter gastroenteritis became an increasingly significant health problem in intensive aquaculture in China. In this study, three bacterial strains were isolated from the intestinal tract of farmed grass carp (Ctenopharyngodon idellus), and were tentatively numbered C9414, C0520 and C0934, and then they were identified as Citrobacter freundii, C. gillenii and C. werkmanii by the biochemical properties and molecular techniques. The strain C9414, namely C. freundii showed the pathogenicity to mice and zebrafish, respectively. Furthermore, the fingerprint patterns with distinct bands of three isolates were generated by single-strand conformation polymorphism (SSCP) analysis. To our knowledge, this is the first report on the bacteria Citrobacter spp. isolated from the intestine of fish in China. [Copyright &y& Elsevier]

mple studies have been conducted to investigate the population genetic structure of grass carp Ctenopharyngodon idella in the Yangtze River, China. However, samples from the upper reaches were not included. In this study, we collected samples from the entire river, including three locations in the upper reaches: Yibin, Banan and Yunyang, two locations in the middle reaches: Shishou and Ruichang and one location in the lower reaches: Hanjiang, and sequenced three mitochondrial coding genes (ND5, ND6 and Cyt b) and one control region (i.e., the D-loop). Nineteen haplotypes were observed in grass carp of the Yangtze River through the analysis of combined sequence data sets (around 4428 bp). Haplotype diversity indices (0.6000 ∼ 0.9333) and nucleotide diversity indices (0.0002 ∼ 0.0020) demonstrated low genetic diversity in the Yangtze grass carp. The analysis of molecular variance and the fixation index ( F = 0.0202) revealed insignificant genetic difference between samples from different reaches. Two monophyletic lineages of haplotypes were identified, with the lineage A experiencing potential expansion events. Along with previous findings, this study provides a better understanding of genetic diversity and variation of grass carp in the Yangtze River and will be served as an important baseline to evaluate the long-term impact of the Three Gorges Dam and other hydroelectric facilities on fish biodiversity. [ABSTRACT FROM AUTHOR]

Thirty-four microsatellite DNA loci were developed for grass carp (Ctenopharyngodon idella) and used to determine the diversity of 42 individuals of grass carp and 16 individuals of black carp collected from Jingzhou fragment (the middle reach) of Yangtze River. All the 34 loci were polymorphic in grass carp. The number of alleles found in grass carp at these loci ranged from 2 to 24. The observed and expected heterozygosities varied from 0.238 to 1.000 and from 0.162 to 0.945, respectively. Thirty of the 34 loci cross-amplified the DNA of black carp (Mylopharyngodon piceus), and 21 of them revealed polymorphism (more than one allele each locus). [ABSTRACT FROM AUTHOR]

Grass carp (Ctenopharyngodon idella), one of the most important freshwater food fish, has made a great contribution to freshwater aquaculture in China. Though a consensus linkage map of grass carp has been reported, the low marker resolution limited its application in fine mapping quantitative trait loci (QTL) of commercially important traits. In this study, a high-density linkage map was constructed based on a full-sib F 1 family of grass carp, which was further used for mapping QTL for five growth related traits: body weight (BWE), body length (BL), body width (BWI), body height (BH) and fatness (FN). This high-density genetic map was constructed with 3979 SNPs, consisting of 24 linkage groups (LGs). The total length of the linkage map was 1752.742 cM, with an average marker resolution of 0.44 cM. QTL mapping analysis detected two significant and 19 suggestive QTL for the five morphometric traits, distributed on 8 LGs. The phenotypic variations explained of these QTL ranged from 7.2% to 32.8%. Finally, comparative genomic analysis revealed that 23 out of the 24 LGs of grass carp showed high synteny with 23 chromosomes of zebrafish. Taken together, the high-density linkage map and the 21 growth-related QTL, provide valuable genomic resources for both marker-assisted selection (MAS) and comparative genomic studies in grass carp and its related species. • The genetic linkage map for grass carp with an average resolution of 0.44 cM per locus was constructed using 3979 SNPs. • 21 QTL related to body weight, body length, body width, body height and fatness were identified on three linkage groups. • The synteny analysis between this genetic map and zebrafish genome showed high synteny. [ABSTRACT FROM AUTHOR]

Two trypsin isoforms (GT-A and GT-B) from the grass carp ( Ctenopharyngodon idellus) intestine were isolated and purified. SDS-PAGE electrophoresis showed that GT-A and GT-B had relative molecular masses of 30,740 and 26,400, respectively. Enzyme activity was inhibited by three organic trypsin inhibitors but not by EDTA. They had optimal pH of 8.0 and 8.5, and optimal temperatures of 38.5 and 44.0°C, respectively, when hydrolyzing N–benzoyl- l-arginine ethyl ester·HCl (BAEE). They lost 95.8 and 93.7% of their activities, respectively, after heating for 20 min at 65°C. Their thermal denaturation temperatures, respectively, were 66.3 and 67.3°C. GT-A has a Km value of 21.2 μM and a Vmax of 2.0 × 103 min−1, and GT-B has a Km value of 31.7 μM and a Vmax of 3.3 × 103 min−1. Their physiological efficiencies were 94.3 and 105.3 μM−1 min−1, respectively. The Arrhenius activation energies of GT-A and GT-B were 4.16 and 4.38 kcal/mol, respectively. The activities of GT-A and GT-B were not activated by Ca2+, but their thermostability was improved in the presence of Ca2+. Enzyme activity was reduced in presence of Zn2+, Cu2+, Hg2+ and Al3+. Thermal stabilities of GT-A and GT-B were intermediate between Arctic and tropical fish species, and consistent with the wide range of water temperatures to which grass carp are exposed in most provinces of China. [ABSTRACT FROM AUTHOR]

Grass carp (Ctenopharyngodon idellus) is one of the most important freshwater cultural species in China. However, obesity, fatty liver and digestive tract inflammation commonly exist in commercial grass carp, which may be due to excessive food and energy intake in daily feeding. Therefore, the feeding strategy should adapt to fish appetite, nutrition requirements and welfare in intensive aquaculture. To investigate the effects of feeding frequency on growth, physiology and metabolism-related fgf21 expression to provide a reference for the selection of feeding strategy, healthy and homogeneous juvenile grass carp (45.2 ± 2.5 g) were randomly divided and adapted to four feeding frequencies of 1, 2, 3 or 4 times/day following satiated feeding for 8 weeks. The growth rate increased with increasing feeding frequency. The hepatosomatic and abdominal fat-somatic indexes were higher in the higher feeding frequency groups, while the gut-somatic index was higher in the low feeding frequency groups (P < 0.05). The actual feeding ration increased from 1.3% to 3.5% with increasing feeding frequency (P < 0.05), and the feed conservation ratio increased from 1.5 to 2.3, but there was no significant difference between 3 and 4 meals/day (P ˃0.05). The levels of serum glucose, triglycerides and total cholesterol also increased with increasing feeding frequency, while glycogen levels were higher in the 1 time/day group in both liver and muscle. The activities of digestive enzymes were higher in the high feeding frequency groups. Fgf21 gene expression was relatively low in the low feeding frequency group in all tissues, and the expression levels increased with increasing feeding frequency in the liver and muscle. Overall, the optimal feeding frequency to enhance the growth and health of juvenile grass carp is 3 times/day under apparent satiation. • The optimal feeding frequency for juvenile grass carp is 3 times/day under apparent satiation. • High feeding frequency had adverse effects for grass carp with artificial diets. • The feed intake of each meal was differ under various feeding frequencies. • The expression of fgf21 responded to different feeding frequency, especially in muscle and liver. [ABSTRACT FROM AUTHOR]

Flavobacterium columnare is the causal agent of columnaris disease and has severe impacts on the grass carp, Ctenopharyngodon idellus, aquaculture industry. The genetic characteristics of F. columnare strains isolated from grass carp in China are not clear. Therefore, in this study, we obtained 45 bacterial isolates from grass carp with columnaris disease from 11 provinces of China. The 45 bacterial isolates were identified as F. columnare according to phenotypic traits, biochemical characteristics, and molecular identification with 16S rDNA gene sequencing. Furthermore, based on the analysis of restriction fragment length polymorphism of the 16S rDNA gene (16S-RFLP), 37 isolates belonged to genomovar I, 5 isolates were ascribed to genomovar II, and 3 isolates were identified as genomovar III. Phylogenetic analysis further confirmed the genetic differences between the three genomovar isolates and revealed a closer relationship between genomovar I and II isolates. The colony pseudo-root morphology and the degree of bacterial aggregation of the three genomovar isolates were significantly different when they were cultured under the same conditions. We concluded that there are three genotypes of F. columnare currently identified in grass carp, and genomovar I was the main type. These findings provide a basis for the genetic diversity of F. columnare in grass carp in China. • We conducted a survey of columnaris disease of grass carp in 11 provinces of China. • Forty-five bacterial strains were isolated and identified as Flavobacterium columnare. • Three types of genomovars (I, II, III) were identified from the 45 F. columnare strains. • The colony pseudo-root and bacterial aggregation of the three genomovar strains were different. [ABSTRACT FROM AUTHOR]

Grass carp reovirus (GCRV) leads to severe hemorrhagic disease in grass carp (Ctenopharyngodon idella) and causes economic losses in grass carp aquaculture. Recent epidemiological investigations showed that GCRV genotype II is the dominant subtype in China. Therefore, it is very important to develop a novel vaccine for preventing diseases caused by GCRV genotype II. In this study, we employed a bac-to-bac expression system to generate GCRV-II-based virus-like particles (VLPs). Previous studies have shown that the structural proteins VP3, VP4, and VP38 encoded by the segments S3, S6, and S10 of type II GCRV are immunogenic. Hence, the GCRV-VLPs were produced by co-infection of sf9 cells with recombinant baculoviruses PFBH-VP3, PFBH-VP4, and PFBH-VP38. The expressions of VP3, VP4, and VP38 proteins in GCRV-VLPs were tested by IFA and Western blot analysis. By electron microscopic observations of ultrathin sections, purified VLPs showed that the expressed proteins are similar in shape to GCRV genotype II with a size range from 40 nm to 60 nm. The immunogenicity of GCRV-VLPs was evaluated by the injection immunization of grass carp. The analysis of serum-specific IgM antibody showed that grass carp immunized with GCRV-VLPs produced GCRV-specific antibodies. Furthermore, injection with GCRV-VLPs increased the expressions of immune-related genes (IgM, IFN, TLR3, TLR7) in the spleen and kidney. In addition, grass carp immunized with a GCRV-VLPs-based vaccine showed a relative percent survival rate (RPS) of 83.33% after challenge. The data in this study showed that GCRV-VLPs demonstrated an excellent immunogenicity and represent a promising approach for vaccine development against GCRV genotype II infection. [ABSTRACT FROM AUTHOR]

Here we report the isolation and characterization of 17 polymorphic loci isolated from a partial genomic DNA library of grass carp ( Ctenopharyngodon idellus) enriched for CA repeats. We tested variability of these microsatellites on 24 unrelated individuals collected in China. All microsatellites were polymorphic. The average allele number was 7.9 per locus, ranging from four to 13. The observed heterozygosity was from 0.46 to 0.88 with an average of 0.71, whereas the average expected heterozygosity was 0.78. Sixteen of the 17 microsatellites conformed to Hardy–Weinberg equilibrium, and inherited independently. These microsatellites can be used to study genetic diversity and population structure of wild populations, and facilitate selective breeding of cultured broodstocks. [ABSTRACT FROM AUTHOR]

Grass carp is one of the most important freshwater aquaculture species in China. However, the mechanisms underlying the growth of muscle tissue in the fish are unclear. High-throughput RNA-Seq was used to analyze the transcriptome of grass carp muscle tissue between fast- and slow-growing fish family groups. Twenty-four individuals each from 4 fast-growing families and 4 slow-growing families were used to reduce background noise. 71 up-regulated and 35 down-regulated genes were identified in the differentially expressed genes (DEGs). GO and KEGG enrichment analyses revealed the DEGs were involved in the GH/IGF axis, calcium metabolism, protein and glycogen synthesis, oxygen transport, cytoskeletal and myofibrillar components. IGFBP1 was up-regulated in big fish while GHR2 was down-regulated. Glutamic pyruvate transaminase 2, an indicator of liver tissue damage, was down-regulated in big grass carp, which indicates that the fish was better adapted to an artificially formulated diet. GAPDH, the rate-limiting enzyme in glycolytic flux was highly expressed in fast-growing grass carp, reflecting enhanced carbohydrate metabolism. Higher expression of ALAS2 and myoglobin 1 in big grass carp, related to oxygen transport might promote aerobic exercise along with food intake and muscle growth. Genes for cytoskeletal and myofibrillar components such as tropomyosin, meromyosin, and troponin I were also up-regulated in big grass carp. These results provide valuable information about the key genes for use as biomarkers of growth in selective breeding programs for grass carp and contribute to our understanding of the molecular mechanisms and regulative pathways regulating growth in fish. Unlabelled Image • Transcriptomes of grass carp muscle tissue between fast- and slow-growing fish family groups were compared. • Between-group comparisons revealed 106 genes that were significantly differential expressed (DEGs). • DEGs were involved in GH/IGF axis, calcium metabolism, oxygen transport, myofibrillar components et al. • The results provide valuable information about the key genes for use as biomarkers of growth in grass carp. [ABSTRACT FROM AUTHOR]

In this work, the effects of substrates on volatile flavor compounds of Shanghai smoked fish (SSF) from grass carp was investigated by head space-solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) by changing the ratios of soy sauce (15%-25%) to white sugar (10%-20%) and replacing white sugar with reducing sugar (glucose, fructose, and ribose). The results showed the key volatile flavor compounds (ROAV ≥ 1) of SSF were 2,4-decadienal, p-xylene, nonanal, and 1-octen-3-ol with the relative contents of 10.33, 1.14, 4.84, and 1.76%, respectively. Furthermore, the existence of soy sauce had an enhancing role in the production of pyrazines, but no significant difference in white sugar. The contents of isovaleraldehyde and benzeneacetaldehyde were increased when white sugar was replaced with glucose, octanol, and 2-pentyl furan for fructose, no obvious difference in ribose. Moreover, the optimal ratios of soaking solutions were 20% soy sauce and 15% white sugar based on the scoring method of sensory evaluation. This study will provide a theoretical basis for the formation of volatile flavor compounds of SSF. PRACTICAL APPLICATIONS: Grass carp usually grows in freshwater such as pond or lake, but bacteria with earthy smell are easily attached to plankton such as diatom and cyanobacteria leading to the accumulation of bad odor substances through the food chain. Shanghai smoked fish (SSF) deeply loved by public is a traditional special dish with crispy crust and delicious taste. The attractive flavor of grass carp could be increased with the help of the Maillard reaction (MR) and seasonings. Therefore, the effect of the MR on the volatile flavor compounds of SSF was investigated by HS-SPME-GC/MS in this work. A detailed study on the volatile flavor compounds of Shanghai smoked fish could not only enrich the theoretical knowledge of flavor chemistry of freshwater fish, but have a profound contribution to the development of freshwater fish processing techniques., (© 2020 Wiley Periodicals LLC.)

In 2019, an epidemic of ulcerative lesions emerged in grass carp (Ctenopharyngodon idellus) in the Yangtze River basin of China. Diseased fish displayed hemorrhagic ulcers of the tail muscle and reach 70% cumulative mortality, causing serious economic losses. The objective of the present study is to describe disease characteristics, analyze disease factors, and elucidate the etiology. Diseased fish from Qingbaijiang and Deyang, Sichuan, were dissected for the necropsy, pathology, and microbiology investigation. The histopathological examination revealed that the target organs of grass carp were muscle, spleen, and kidney, all showing severe necrosis and varying degrees of inflammation and edema. There were slight changes in the intestine, liver, gill, and heart. Nine strains of bacteria were isolated from diseased grass carp and were identified as belonging to four Aeromonas species. Subsequently, symptoms of tail muscle hemorrhage similar to the clinical symptoms were duplicated through re-infection. There was also a period of low temperatures in the affected regions in the early spring of 2019. Based on the results, we concluded that the genus Aeromonas was the pathogen causing the grass carp epidemic ulcerative disease, which perhaps links to the temperature abnormality. • An epidemic emerged in grass carp with ulcerative lesion was studied. • Inferred to be an infectious pathogenic disease by pathological studies. • Nine strains of bacteria were isolated and identified as genus Aeromonas. • The similar symptoms to nature were duplicated by the re-infection. • The epidemic perhaps links to the continuous low temperature. [ABSTRACT FROM AUTHOR]

A novel Gram-negative bacterium, designated CFH 10530 T , was isolated from the intestine of grass carp. The sample was collected from the aquaculture training base at the College of Fisheries, Henan Normal University, Xinxiang, PR China. Cells of strain CFH 10530 T were coccoid, ovoid or short-rod-shaped, aerobic, non-spore-forming and non-motile. 16S rRNA gene sequence analysis demonstrated that strain CFH 10530 T was closely related to Paracoccus endophyticus SYSUP0003 T (97.7 % sequence similarity), Paracoccus halophilus HN-182 T (96.5 %) and Paracoccus panacisoli DCY94 T (96.1 %). The strain grew optimally at 25-28 °C, at pH 7.0 and with 0-2 % (w/v) NaCl. Cells were positive for catalase and oxidase, nitrate was reduced and H 2 S was not produced. The isoprenoid quinone was Q-10. Major cellular fatty acids were summed feature 8, C 18 : 0 and C 18 : 0 3-OH. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, one unidentified aminolipid and five unidentified polar lipids. The genome size was 3 331 229 bp with a G+C content of 69.6 mol%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between CFH 10530 T and the other species of the genus Paracoccus were found to be below the recommended levels for species delineation (ANIm <85, ANIb <80 and dDDH <24 %). Based on its physiological properties, chemotaxonomic characteristics and low ANI and dDDH results, strain CFH 10530 T is considered to represent a novel species for which the name Paracoccus luteus sp. nov., is proposed. The type strain is CFH 10530 T (=KCTC 62919 T =CGMCC 1.16597 T ).

This study aimed to determine the plasma and tissue residue depletion kinetics of doxycycline (DC) in grass carp (Ctenopharyngodon idella) after daily oral administrations at 20 mg/kg for 3 days, and to calculate the corresponding withdrawal times. Following drug administrations, samples of plasma, liver, kidney, gill and muscle + skin were collected at predetermined time points (0.25, 0.5, 1, 3, 5, 7, 14, 21, 28, 35, 42, 49 and 56 days) and analyzed for concentrations of DC using a LC-MS/MS method. The results showed that liver had the highest concentrations and the slowest depletion compared to other tissues, with detectable DC up to 49 days (58.9 ± 12.8 μg/kg). The WT 1.4 software and "reschem" package were used to calculate withdrawal times, and the results were similar. The results suggest a withdrawal time of 41 days for Europe and China and 50 days for Japan is needed for DC in grass carp after 3 daily oral administrations at 20 mg/kg. Overall, this study improves our understanding of the tissue residue depletion kinetics of DC in fish, and the results may help regulatory agencies to determine proper withdrawal periods based on different regulatory standards in different countries to ensure safety of aquatic food products., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Background: Lactobacillus plantarum, a versatile lactic acid-fermenting bacterium, isolated from the traditional pickles in Ningbo of China, was chosen for grass carp fermentation, which could also improve the flavor of grass carp. We here explored the central metabolic pathways of L. plantarum by using metabolomic approach, and further proved the potential for metabolomics combined with proteomics approaches for the basic research on the changes of metabolites and the corresponding fermentation mechanism of L. plantarum fermentation., Results: This study provides a cellular material footprinting of more than 77 metabolites and 27 proteins in L. plantarum during the grass carp fermentation. Compared to control group, cells displayed higher levels of proteins associated with glycolysis and nucleotide synthesis, whereas increased levels of serine, ornithine, aspartic acid, 2-piperidinecarboxylic acid, and fumarate, along with decreased levels of alanine, glycine, threonine, tryptophan, and lysine., Conclusions: Our results may provide a deeper understanding of L. plantarum fermentation mechanism based on metabolomics and proteomic analysis and facilitate future investigations into the characterization of L. plantarum during the grass carp fermentation.

In this study, a full-sib population of Ctenopharyngodon idella was constructed and approximately 500 C. idella individuals were sampled at four early developmental stages (hatching, first feeding, juvenile fish and young fish). Four DNA pools were constructed and subjected to next-generation sequencing. On the basis of the identification of single nucleotide polymorphisms (SNP), changes in gene and genotype frequencies during the developmental progress of C. idella were revealed, which indicates that death during the early developmental stage is not a random process. These findings will establish the basis for further studies performed for identifying superior alleles or genotypes as target markers for molecular breeding., (© 2018 The Fisheries Society of the British Isles.)

Grass carp reovirus (GCRV), the most pathogenic aquareovirus, can cause fatal hemorrhagic disease in fingerling and yearling grass carp. Vaccination by injection is by far the most effective method of combating disease. However it is labor intensive, costly and not feasible to vaccinate large numbers of the fish. Thus, an efficient and economic strategy for the prevention of GCRV infection becomes urgent. Here, functionalized single-walled carbon nanotubes (SWCNTs) as carrier were used to manufacture SWCNTs-VP7 subunit vaccine with chemical modification. Different developmental stages of grass carps were immunized by VP7/SWCNTs-VP7 subunit vaccine against GCRV by intramuscular injection and bath immunization. The results indicate that better immune responses of grass carp immunized with the SWCNTs-VP7 subunit vaccine were induced in comparison with VP7 subunit vaccine alone. Immunization doses/concentrations are significantly reduced (about 5-8 times) to prevent GCRV infection in different developmental stages of grass carp with injection or bath treatment when SWCNTs carrier was used. A good immune protective effect (relative percentage survival greater than 95%) is observed in smaller size fish (0.2 g) with SWCNTs-VP7 bath immunization. In addition, serum respiratory burst activity, complement activity, lysozyme activity, superoxide dismutase activity, alkaline phosphatase activity, immune-related genes and antibody levels were significantly enhanced in fish immunized with vaccine. This study suggested that functionalized SWCNTs was the promising carrier for recombinant subunit vaccine and might be used to vaccinate fish by bath approach., (Copyright © 2014 Elsevier Ltd. All rights reserved.)