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1.
Visceral white nodules disease (VWND) caused by Pseudomonas plecoglossicida is a common disease in cage-farmed large yellow croaker (Larimichthys crocea) in China. VWND usually occurred at water temperature of 16–19℃, resulting in high mortality in farmed large yellow croaker. Now, P. plecoglossicida as its pathogen has been considered nonpathogenic at 7–12℃. During February 2019, an infectious disease outbreak was observed in cage-farmed large yellow croaker at a water temperature of 12℃ in Ningde, China. This disease is characterized by white granulomatous lesions in internal organs of the diseased fish, which was similar with the symptoms of the VWND in large yellow croaker. Then, we isolated a bacterial strain named PQLYC4 from visceral lesions of the diseased fish. The experimental infection studies demonstrated that the strain PQLYC4 was the pathogen of the disease, which was further identified as P. plecoglossicida by the analysis of morphology, 16s rRNA gene homology and average nucleotide identity based on the whole genome sequence. Our results revealed that P. plecoglossicida strain PQLYC4 could cause the outbreak of the VWND at 12℃, a water temperature lower than that reported previously, thus providing new knowledges of prevalence and prevention of the VWND in large yellow croaker.  相似文献   

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4.
Unusual persistent natural mortality occurred in a floating in‐pond raceway system intensively stocked with channel and hybrid catfish beginning in early November 2016 up until March 2017. The temperature during the period of outbreak ranged from 7.2 to 23.7°C. Gross examination of freshly dead and moribund fish revealed pale gills, slight abdominal distension and swollen inflamed vents. Comprehensive necropsy of 20 fish demonstrated vast amounts of bloody ascitic fluid in the coelomic cavity, visceral congestion, splenomegaly and pale friable livers but macroscopically normal kidneys, suggesting systemic bacterial infection. Bacterial cultures were initiated from skin, gills and major internal organs. Following incubation, a mixture of three bacterial colony phenotypes was observed on agar plates. Presumptive biochemical characterization of the isolates followed by 16S‐rRNA sequence analysis resulted in the identification of Aeromonas veronii, Streptococcus parauberis and Shewanella putrefaciens. Channel catfish juveniles were experimentally infected with the recovered isolates to fulfil Koch's postulates. Moreover, an antibiogram was used to evaluate the susceptibility of the isolates to antimicrobial drugs approved for use in aquaculture. Aquaflor was used successfully for treatment. Here, we report bacterial coinfection lead by A. veronii and the first identification of S. parauberis and S. putrefaciens from cultured catfish in North America.  相似文献   

5.
The disease outbreaks in aquaculture system of wetlands are the major cause of fish mortality. Among various bacterial septicaemic diseases, fish mortality caused by Acinetobacter spp. is recently reported in different fish species. Fish disease outbreak was investigated in a wetland of West Bengal, India to identify the aetiological factors involved. The moribund fish were examined and subjected to bacterial isolation. Two bacterial causative agents were identified as Acinetobacter junii and Acinetobacter pittii by biochemical characterization and 16S rRNA gene amplification. Both the isolates were oxidase‐negative, nitrate‐negative, catalase‐positive and indole‐negative. The molecular identification using 16S rRNA gene sequencing and phylogenetic tree analysis further confirmed the two Acinetobacter spp. with 97%–99% similarity. The antibiotic resistance patterns of these two bacteria revealed that both of them were resistant to β‐lactam, cefalexin, cephalothin, amoxyclav, cefuroxime, cefadroxil, clindamycin, vancomycin and penicillin. In addition, A. pittii was also resistant to other antibiotics of cephams group such as ceftazidime and cefotaxime. In the challenge experiment, both A. junii and A. pittii were found to be pathogenic with LD50 of 1.24 × 105 and 1.88 × 107 cfu/fish respectively. Histopathological examination of gill, liver and kidney revealed prominent changes supporting bacterial septicaemia. The investigation reports for the first time on concurrent infection by A. junii and multidrug‐resistant (MDR)‐A. pittii as emerging fish pathogens to cause severe mortality in Labeo catla and Hypophthalmichthys molitrix in a freshwater wetland.  相似文献   

6.
Pseudomonas plecoglossicida NB2011, the causative agent of visceral granulomas disease in farmed Larimichthys crocea in China, encodes a predicted type three effector PP_ExoU, a homolog of the cytotoxin ExoU of Pseudomonas aeruginosa. In this study, secretion of PP_ExoU was tested in various broth, the protein was expressed with the pET30a prokaryotic system, the phospholipase A (PLA) activity of the recombinant protein was determined with fluorogenic phospholipid substrates, fusion expression with green fluorescent protein in transfected HeLa cells was investigated, and the lactate dehydrogenase (LDH) level was measured. The results showed the protein was type three secreted in several media; the recombinant protein displayed significant PLA1 activity with ubiquitin. Fluorescence was observed on the cell membrane and scattered in the cytoplasm of HeLa cells expressing catalytic wild‐type PP_ExoU, blebbing and stretching developed in the cell membranes indicating of membrane damage. Fluorescence scattered in the cytoplasm of cells expressing the catalytic inactive protein. A significant LDH level was detected in HeLa cells expressing wild‐type PP_exoU, but not in the Ser/Asp‐mutated protein, suggestion mutation of predicted catalytic residues abolished the PLA activity. This is the first report on the function of a secreted type three protein from P. plecoglossicida.  相似文献   

7.
Interaction between bacterial pathogen and aquatic animal host is exceedingly complex, which involves large dynamic changes in gene expression during different stages of the disease. However, research on identifying key virulence genes based on the dynamics of gene expression changes of a one‐sided bacterial pathogen in tissue has not been reported so far across different stages of infectious disease. The clpV for the T6SS of Pseudomonas plecoglossicida was identified for a candidate for key virulence gene based on dynamic changes of gene expression. For the Epinephelus coioides infected using clpV‐RNAi strain, no deaths were observed up to 20 dpi. The spleens, kidneys and livers of all the E. coioides that received clpV‐RNAi strain failed to develop visible nodules at 5–8 dpi, with the swelling gradually disappearing. The burdens of clpV‐RNAi strain in the spleen and blood were greatly reduced at most of the time points after injection, and the burdens of clpV‐RNAi strain in the head kidneys and trunk kidneys also had a sharp reduction from 72 to 120 hpi. This paper provides a new insight into the discovery of key virulence genes of pathogens in infected tissue systems.  相似文献   

8.
An 8‐week feeding experiment was conducted to investigate the effects of dietary glycyrrhizic acid (GA) on growth, survival and immune response of juvenile large yellow croaker, in seawater floating net cages. GA was supplemented into the basal diet to formulate four isonitrogenous and isoenergetic practical diets containing 0.00% (the control diet), 0.01%, 0.02% and 0.04% GA of dry weight, respectively. Triplicate groups of 60 fish were fed to apparent satiation by hand twice daily. The results showed that the specific growth rate, survival rate and feed efficiency ratio revealed no significant differences among dietary treatments (P > 0.05). The phagocytic index of head kidney macrophage was significantly increased by the supplementation of 0.04% dietary GA compared to the control group (P < 0.05). Fish fed 0.04% dietary GA also showed significantly higher serum lysozyme activity than fish fed the control diet and diet with 0.01% GA (P < 0.05). The cumulative mortality rate after natural infestation of parasites (protozoan, Cryptocaryon irritans Brown) showed no significant differences among dietary treatments. These results suggested that dietary glycyrrhizic acid improved certain non‐specific immunological parameters of juvenile large yellow croaker. However, GA was not able to protect juvenile large yellow croaker effectively from protozoan infection.  相似文献   

9.
A feeding trial was conducted to determine the dietary threonine requirement of juvenile large yellow croaker (Larmichthys crocea). Six diets were formulated containing 45% crude protein with six graded levels of threonine (0.71–2.46% in about 0.35% increment). Each diet was randomly assigned to triplicate groups of 60 juvenile fish (initial body weight 6.00 ± 0.10 g). Fish were fed twice daily (05:00 and 16:30) to apparent satiation for 8 weeks. The result indicated that significant difference was observed in the weight gain among all treatments. Specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and nitrogen retention (NR) increased with increasing levels of threonine up to 1.75% diet (P < 0.05), and thereafter, declined. No significant differences in body dry matter, crude protein, crude lipid or ash content were found among dietary treatments. Theronine contents of fish muscle were significantly affected by dietary threonine levels (P < 0.05). Fish fed the diet with 0.71% threonine showed the lowest threonine content (2.94%) in fish muscle, while fish fed the diet with 1.75% threonine had the highest value (3.16%). Other essential amino acid contents of muscle were not significantly different among the dietary treatments. On the basis of SGR, FE or NR, the optimum dietary threonine requirements of juvenile L. crocea were estimated to be 1.86% of diet (4.13% of dietary protein), 1.90% of diet (4.22% of dietary protein) and 2.06% of diet (4.58% of dietary protein), respectively, using second‐order polynomial regression analysis.  相似文献   

10.
Over‐winter fasting and man‐made food deprivation to increase meat quality are common in the process of large yellow croaker (Larimichthys crocea) aquaculture. This study aimed to determine the changes in lipoprotein lipase (LPL) and fatty acid synthetase (FAS) activities and mRNA expressions, and the relationships between these changes and fat content in large yellow croaker liver and muscle tissues during fasting. A total of 2933 bp LPL cDNA, including an open reading frame of 1533 bp encoding 510 amino acids, and a 1233 bp fragment of FAS cDNA coding 411 amino acids were cloned. Expressions of both genes were ubiquitous. During a 35‐day fasting period, the hepatosomatic index and fat content in muscle and liver were significantly decreased (P < 0.05). mRNA levels of LPL increased significantly during the fasting period except the first 3 days, and FAS mRNA levels decreased significantly in both muscle and liver (P < 0.05) although there were some fluctuations. Muscle and liver LPL activities were significantly higher following fasting for 7 days, decreased to the initial value following fasting for 14 days, and elevating significantly afterwards (P < 0.05). FAS activities in muscle and liver maintained a significantly decreasing trend during the short‐term fasting (P < 0.05) and kept obviously rising thereafter (P < 0.05). Activities and mRNA levels of both LPL and FAS were not always consistent, which implied that both pre‐translational and post‐translational regulations existed during fasting. Our results suggest that the reasonable fasting time is 21 days before harvesting when fat content decreased significantly.  相似文献   

11.
A 65‐day feeding trial was conducted to investigate the effects of dietary antimicrobial peptide APSH‐07 on the growth performance, anti‐oxidation responses, stress resistance and intestine microbiota of large yellow croaker Larimichthys crocea. Four isonitrogenous and isolipidic diets were formulated with 0, 30, 60 and 90 mg/kg of APSH‐07, respectively. The results showed that the fish fed with 90 mg/kg of dietary APSH‐07 had the significantly highest specific growth rate (p < .05). The activities of catalase, superoxide dismutase, the total anti‐oxidative capacity and lysozyme had the significantly highest values in liver of fish fed with 90 mg/kg of dietary APSH‐07 (p < .05). Serum glucose increased significantly in fish fed diets without APSH‐07 supplementation after temperature stress, while serum cortisol increased significantly in those after trawl stress (p < .05). Fish fed with 90 mg/kg of dietary APSH‐07 showed significantly higher operational taxonomic units, ACE estimator and phylogenetic diversity whole tree in intestine microbiota compared to fish fed without APSH‐07 (p < .05). In conclusion, under the present experimental condition, 90 mg/kg of antimicrobial peptide APSH‐07 supplementation in diet had the better growth performance, higher anti‐oxidation and stress resistance capacity, and a potentially more beneficial intestine microbial community of large yellow croaker.  相似文献   

12.
An 8‐week feeding trial was conducted to evaluate the effect of replacement of fish meal (FM) with fermented soybean meal (FSM) on growth performance, intestinal morphology and microbiota of juvenile large yellow croaker (Larimichthys crocea). Replacement ratio of FM with FSM were 0%, 15%, 30%, 45%, 60% and 75%, respectively (marked as FSM0, FSM15, FSM30, FSM45, FSM60 and FSM75). The results indicated that the survival ranged from 84.78% to 99.44%, and no significant differences were observed among all treatments (p > 0.05). Weight gain ratio (WGR) and specific growth rate (SGR) significantly decreased when the replacement level of FM protein exceeded 60%, and fish fed the FSM60 and FSM75 diets had lower WGR and SGR than those fed the other diets. Feed intake (FI) and feed conversion rate (FCR) significantly increased with replacement levels of FM increasing. Illumina high‐throughput sequence analyses showed that the alpha diversity did not differ among the diets of FSM0, FSM15 and FSM75. The whole community of tested samples was not modified by FSM, Firmicutes and Proteobacteria were the dominant flora in the intestines based on the phyla level. The dominant phyla in the water sample were Proteobacteria, Bacteroidetes. Fish fed the diet containing FSM75 significantly reduced the species abundance of Paenibacillus. There was a certain correlation between the intestine microbiota and SGR, antioxidant, and immune. Results indicated that up to 45% of FM can be replaced by FSM without negative effects on growth performance and intestinal integrity of juvenile large yellow croaker.  相似文献   

13.
This study was conducted to compare lipid deposition pattern of three fish species among fish size, Large yellow croaker (Larmichthys crocea), Japanese seabass (Lateolabrax japonicus) and Turbot (Scophthalmus maximus L.), Using magnetic resonance imaging technology for adult fish, results showed that lipid of large yellow croaker mainly deposits in abdominal cavity wall, while for Japanese seabass mainly deposit in visceral adipose tissue and for turbot lipid mainly distribute subcutaneous tissue. Three sizes for each species were selected: S1 (small size), S2 (intermediate size) and S3 (big size), to examine chemical analysis. Results of chemical analysis indicated that whole body lipid content of large yellow croaker significantly increased with the increase in body weight, but Japanese seabass and turbot significantly decreased (p < .05). Lipid content of muscle and intestinal tract in large yellow croaker significantly increased with the increase in body weight (p < .05), but lipid content of adipose tissue, kidney, heart and skin in S2 group were higher than S1 and S3 groups (p < .05). Lipid content of liver, eye, kidney and brain in Japanese seabass significantly increased with the increase in body weight (p < .05), but lipid content of stomach and heart showed an opposite trend. Lipid content of liver, adipose tissue, skin and eye in turbot significantly decreased (p < .05), but lipid content of brain significantly increased with the increase in body weight (p < .05). The results indicated that lipid content of different tissues in fish presented different trends, which was species‐dependent.  相似文献   

14.
A disease outbreak in farmed Atlantic cod caused by Yersinia ruckeri is reported. Mortality started following vaccination of cod reared in two tanks (A and B). The accumulated mortality reached 1.9% in A and 4.8% in B in the following 30 days when treatment with oxytetracycline was applied. Biochemical and molecular analysis of Y. ruckeri isolates from the cod and other fish species from fresh and marine waters in Iceland revealed a high salinity‐tolerant subgroup of Y. ruckeri serotype O1. Infected fish showed clinical signs comparable with those of Y. ruckeri ‐infected salmonids, with the exception of granuloma formations in infected cod tissues, which is a known response of cod to bacterial infections. Immunohistological examination showed Y. ruckeri antigens in the core of granulomas and the involvement of immune parameters that indicates a strong association between complement and lysozyme killing of bacteria. Experimental infection of cod with a cod isolate induced disease, and the calculated LD50 was 1.7 × 104 CFU per fish. The results suggest that yersiniosis can be spread between populations of freshwater and marine fish. Treatment of infected cod with antibiotic did not eliminate the infection, which can be explained by the immune response of cod producing prolonged granulomatous infection.  相似文献   

15.
Pseudomonas plecoglossicida is associated with multiple fish diseases, and temperature is one of the most important environmental factors related to its outbreak. To elucidate the influence of temperature variation on the pathogen, the global metabolomics of P. plecoglossicida (NZBD9) were analysed at the virulent (18°C) and avirulent (12°C and 28°C) temperatures. The result showed that the levels of Phosphoric acid, Tyrosine, Spermidine and Sucrose were significantly reduced,while Itaconic acid, Glucaric acid and Isomaltose were increased in P. plecoglossicida at 18°C. These metabolic adjustments assist P. plecoglossicida to survive in adverse environments, proliferate in the host, colonize and resist host immune clearance during the initial steps of infection. The results suggested that L321_03626 and L321_18122 genes played a key role in the regulation of these metabolic adaptions and thus regulated P. plecoglossicida virulence at virulent temperature, which was proved by further gene silencing and artificial infection. The present study, for the first time, determines the P. plecoglossicida metabolomic responses to temperature variation, which is helpful to explore its pathogenic mechanism and provides reference for disease control.  相似文献   

16.
The use of traditional bait and medicament in freshwater aquaculture exacerbates environmental pollution and leads to frequent occurrence of diseases. Effluent collected after Rhodopseudomonas palustris‐mediated wastewater treatment could be reutilized as microbial feeds, medicament and aquaculture water to culture Pelteobagrus vachelli. Therefore, a novel integrated system of wastewater treatment using effluent containing R. palustris that improves yield, increases disease resistance and enhances the quality of aquaculture water for P. vachelli culture was proposed and investigated. P. vachelli can grow well in effluent containing R. palustris (ER). The survival rate, yield and whole‐body composition of the ER group were all increased compared to those of the control group (CK). The biochemical (B vitamin) and other substances in the effluent of R. palustris enhanced the activity of proteases, amylases, lipases, alkaline phosphatase (AKP), acid phosphatase (ACP), phagocytic, superoxide dismutase (SOD) and catalase (CAT) by up‐regulating the expression of AKP, ACP, SOD and CAT genes. Theoretical analysis showed that biochemical substances regulated the expression of these genes and enzyme activities as stimulus signal, component and active centre. Moreover, R. palustris and biochemical substances improved the target of rapamycin (TOR) and nuclear factor kappa B (NF‐κB) signalling pathways and intestinal microbiota. Furthermore, R. palustris inhibited Aeromonas hydrophila, which increased resistance to fish diseases and promoted the growth of intestinal probiotics. Meanwhile, R. palustris in effluent also purified the quality of aquaculture water. Use of this technology simultaneously helped improve aquaculture water quality, reduce water pollution and wastewater discharge and increased the output and disease resistance of P. vachelli.  相似文献   

17.
A 25‐week immersion challenge was conducted exposing Oreochromis mossambicus, Oreochromis aureus and Oreochromis urolepis hornorum to Francisella noatunensis subsp. orientalis (Fno). Two populations were compared for each fish species; ‘resident fish’ were defined as fish maintained in tanks since week 0 of challenge, whereas ‘naïve fish’ were defined as fish added to tanks once temperature in water reached <26 °C at 21 weeks post‐challenge. Fno genome equivalents (GEs) in water were similar in all treatments 1 h post‐challenge; however, significantly lower Fno GEs were detected 2 weeks post‐challenge in all tanks, and the only treatment with detectable Fno GE after 4 weeks of challenge were the O. mossambicus tanks. Twenty‐one weeks post‐challenge, naïve fish were stocked with ‘resident’ cohorts. Over a 4‐week period, mortalities occurred consistently only in O. mossambicus naïve cohorts. Overall presence of granulomas in spleen of survivors was similar (>55%) in all resident populations; however, in naïve populations, only O. mossambicus presented granulomas. Similarly, only O. mossambicus presented viable Fno in the spleen of survivors, and Fno GEs were only detected in O. mossambicus, and in resident O. aureus. In conclusion, the results of this study suggest different susceptibility of tilapia species to piscine francisellosis.  相似文献   

18.
Diploid and triploid hybrids of large yellow croaker (Pseudosciaena crocea, Pc) and Miiuy croaker (Miichthys miiuy, Mm) were produced by interspecific hybridization. The result showed that Pc (♀) and Mm (♂) can be successfully crossed and hybrid offspring of normal hatch rate were produced. In contrast, a lower fertilize and hatch rate were produced for hybrids of Pc (♂) and Mm (♀), and the offspring died day 19 after hatching. To confirm the ploidy of hybrid offspring, we examined the karyotypes of offspring. The result of DNA relative content investigation and genetic relationship analysis demonstrated that the major hybrid offspring were hybrid diploid. In addition, a small number of hybrid were triploid and gynogenesis diploid. Morphological analysis based on the measurable traits data indicated the success of the interspecific crosses. The natural gynogenetic diploid large yellow croaker (PP), diploid hybrids (PM) and triploid hybrids (PPM) were closer to maternal parent (Pc) than paternal parent (Mm). This study provided genetic evidences of the chromosome, DNA content and morphological levels to support the successful establishment of the polyploidy hybrids of Pc (♀) and Mm (♂).  相似文献   

19.
Fish are commonly infected with non‐tuberculous mycobacteria (NTM), which should be regarded as potential pathogens when handling aquarium fish and equipment. This study examined 107 aquarium fish from pet shops. Cultivation of the fish samples using different selective media was conducted for identification of NTM. Isolates were identified using the GenoType Mycobacterium common mycobacteria and additional species assays, sequencing of the 16S rRNA and rpoB genes, and real‐time PCR assay for identification of Mycobacterium (M.) marinum. Among the investigated fish, 79.4% (85/107) were positive for mycobacteria, with 8.2% (7 of 85) having two mycobacterial species present. Among the positive fish, the common pathogens M. marinum, Mycobacterium fortuitum (M. fortuitum group) and Mycobacterium chelonae were identified in approx. 90% of fish and other NTM species in 10%, including Mycobacterium peregrinum/septicum, Mycobacterium gordonae, Mycobacterium arupense, Mycobacterium kansasii, Mycobacterium ulcerans and Mycobacterium setense. The well‐known human pathogen M. marinum was present in 10.6% of the positive fish (9 of 85). The species of mycobacteria identified in the study are not only recognized as aquarium fish pathogens, but can also cause pathology in humans. Microbiological and clinical communities should therefore be sensitized to the role of NTM in infections associated with exposure to aquarium fish.  相似文献   

20.
The present experiment was conducted to evaluate the efficacy of an additive derived from the nature as an alternative of dietary antibiotic in Japanese eel, Anguilla japonica. Six experimental diets were formulated to contain no antibiotics or additive (yellow loess/YL) (control/CON), three graded levels of yellow loess at 5 (YL5), 10 (YL10) and 20 g/kg (YL20), oxytetracycline at 5 (OTC) and amoxicillin at 10 g/kg amoxicillin (AMX) of diet. Weight gain (WG) and specific growth rate (SGR) from fish fed CON or YL5 diets were significantly lower than those of fish fed YL20 or OTC diets. Among non‐specific enzyme, lysozyme activity of fish fed YL20, OTC or AMX was detected to be significantly higher than that from fish fed CON or YL5 diets, whereas superoxide dismutase (SOD) activity of the fish fed CON was significantly lower than that for fish fed other experimental diets. Challenge test with bacteria, Edwardsiella tarda, showed improved disease resistance among the fish fed different levels of natural additive without any statistical difference from those fed antibiotics (OTC and/or AMX) supplemented diets. Therefore, these results demonstrated the potential of natural feed additive, yellow loess to replace oxytetracycline and/or amoxicillin in Japanese eel, A. japonica.  相似文献   

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