Diseased Rainbow Trout Research Articles

Preparation of O-antigen from Yersinia ruckeri Serotype O1 and Use in the Slide Agglutination Test

In this study, it was aimed at early detection of yersiniosis caused by Yersinia ruckeri in rainbow trouts (Oncorhynchus mykiss) using agglutination test. O-antigen of Y. ruckeri isolated from diseased fishes was prepared. This prepared O-antigen was injected into the ear vein of the rabbit. Serum was removed from blood samples taken on 7th and 15th days after the last injection. Thus, the antibody of the Yersinia ruckeri was produced in the rabbit. Titers of the resulting antibodies were determined by microtitering in 96 well-based plates. It was used successfully in the slide agglutination tests by making necessary dilutions according to the titer ratios of the antibodies. We determined that the motile and Gr (-) bacteria isolated from diseased rainbow trout with yersiniozis symptom were Y. ruckeri according to the results of slide agglutination test without any biochemical test. The isolated bacteria were confirmed to be Y. ruckeri with the results of API 20E test kit and PCR test. The antibodies were stored at -20 and -80°C for use subsequent studies.

Transcriptomic responses to yam ( Dioscorea oppositifolia L .) extract dietary supplementation in rainbow trout ( Oncorhynchus mykiss ) liver

Infectious diseases in rainbow trout (Oncorhynchus mykiss) have been seen in rainbow trout farming industry. Yam (Dioscorea oppositifolia L.) has a functional impact upon anti-disease and strengthens immunity. Understanding the molecular mechanisms which occur in rainbow trout in response to yam will be useful to decrease disease-related morbidity and mortality. In the present study, we conducted transcriptome analysis of liver in rainbow trout fed diets including yam extract (0, 0.2% and 0.4%), to identify yam extract-induced genes and pathways. Over 451 million clean reads were obtained from nine liver libraries. Two comparisons were separately implemented between yam extract groups and control group. Using |log2Fold-change|>1 and p-value < .05 as the threshold, a total of 2,693 differentially expressed unigenes (DEGs) were identified, including 1599 up-regulated and 1,094 down-regulated unigenes. The RNA-Seq results were verified by RT-qPCR. DEGs were classified into three categories by GO annotation and functional enrichment analysis: biological process (23 subclasses), cellular component (16 subclasses) and molecular function (16 subclasses). KEGG annotation and classifications of DEGs indicated endocrine system, immune system, lipid metabolism, carbohydrate metabolism and signal transduction pathways include a large number of DEGs. In addition, 526 overlap DEGs in two comparisons were annotated to 174 pathways in KEGG analysis, 7 top significantly enriched pathway terms include chemokine signalling pathway, platelet activation, progesterone-mediated oocyte maturation, insulin signalling pathway, FoxO signalling pathway, cGMP-PKG signalling pathway and sphingolipid signalling pathway. These findings provide valuable information for further analysis of the disease resistance mechanisms of rainbow trout fed yam.

Identification of Chryseobacterium spp. isolated from clinically affected fish in California, USA.

Chryseobacterium spp. (Family Flavobacteriaceae) are emergent fish pathogens in Europe, Asia and North America. In 2016-2017, 7 bacterial isolates were recovered from posterior kidney or spleen of cultured diseased rainbow trout Oncorhynchus mykiss (n = 1), green sturgeon Acipenser medirostris (n = 1), white sturgeon A. transmontanus (n = 2), blue ram cichlid Mikrogeophagus ramirezi (n = 1), and returning fall Chinook salmon O. tshawytscha (n = 2) from different freshwater systems. Bacterial colonies were visible after 24-48 h incubation at 20°C on agar media. Isolates were Gram-negative, rod-shaped, catalase and oxidase positive. Amplification and partial sequence analysis of the 16S rRNA and gyrB genes allocated the microorganisms to the genus Chryseobacterium sharing 97.2-99.6% similarity to 6 described Chryseobacterium spp. at the 16S rRNA locus, and 87.8-99.1% similarity at gyrB. Phylogenetic analyses in conjunction with percent sequence identity suggest some of the recovered isolates may represent novel Chryseobacterium subspecies or species. The pathogenicity of 5 isolates was evaluated experimentally in rainbow trout (n = 60), brown trout Salmo trutta (n = 60) and white sturgeon (n = 36) in flow-through freshwater at 18°C. Approximately 107 CFU fish-1 was injected in the epaxial musculature of anesthetized animals. Limited mortality was observed and no bacteria were recovered from dead or moribund fish post-challenge. Thirty days post-challenge, survivors were euthanized and multiple tissues were collected and fixed for histological analysis. No consistent histopathological changes were observed in challenged or control fish. While results suggest the recovered Chryseobacterium spp. may be opportunistic pathogens, further research is warranted to better understand the role of these bacteria in fish disease.

Effects of Mentha longifolia extract on some blood and immune parameters, and disease resistance against yersiniosis in rainbow trout

The aim of this study was to investigate the effects of horsemint (Mentha longifolia) hydroalcoholic extract on blood parameters, serum, mucosal immune responses, and expression of immunity-related genes in rainbow trout (n = 360; 10.48 ± 0.2 g). The fish were fed with 0.0, 0.1, 0.2, and 0.3% of horsemint extract in 12 aquaria (100 L) with three replicates (each with 30 fish) for 4 weeks. Blood and serum immune indices, mucosal protein pattern, and expression of alpha-tumor necrosis factor (TNF-α) and lysozyme genes were evaluated at the end of feeding trial following challenge with Yersinia ruckeri. The results of measured experimental indices revealed significant differences in both RBC and WBC counts, hematocrit, hemoglobin, complement, lysozyme, neutrophil, respiratory burst, total protein, and albumin among the fish fed with 0.3 and 0.2% of the extract and control group. The number and density of bands were different in the mucosal protein patterns between the fish received M. longifolia extract. Also, the expression of lysozyme and TNF-α genes increased significantly in the extract-fed fish compared to the control. The protective effect of horsemint extract in the challenge of fish with Y. ruckeri in different treatments showed that a 0.2% inclusion level led to significant rises in both blood and serum immune indices. The fish fed with 0.3% of complementary extract presented elevated number and density of mucosal protein pattern bands in comparison to control group. Post-challenge TNF-α gene expression was higher in fish received high levels of horsemint extract than in the control group. Based on the findings, the improvement of hematological and mucosal immunity indices as well as increased expression of lysozyme and TNF-α genes in fish treated with 0.2% of M. longifolia extract could have resulted from the positive effect of this compound on immunogenisity and increased resistance to bacterial disease in rainbow trout.

Detection and Identification of Bacterial Pathogens in Rainbow Trout (Oncorhynchus mykiss) Samples from Fish Farms in Iran

Rainbow trout (Oncorhynchus mykiss) infections are the most important risk factor causing losses in fish farming industry. The aim of the present study was to identify and determine the frequency of bacterial pathogens Streptococcus iniae, S. parauberis, Lactococcus garvieae, L. lactis, Flavobacterium branchiophilum, F. psychrophilum and Yersinia ruckeri in diseased rainbow trout samples collected from different fish farms in Zanjan, Iran. A total of 103 individual diseased rainbow trout including 412 organ samples of liver, kidney, gills and eye organs were collected from 17 fish farms. Overall, 92 (89.3%) out of 103 rainbow trout were positive for the presence of at least one tested pathogen. According to culture and biochemical tests, 199 (48.3%) bacterial isolates were detected. However, molecular analysis confirmed 92.4% (184/199) of isolates. The most common isolated pathogen was L. garvieae (56.3%, 112/199), followed by S. iniae (11.5%, 23/199), F. branchiophilum (9.5%, 19/199) and Y. ruckeri (9.1%, 18/199). Lactococcus lactis and F. psychrophilum were detected with lowest frequency (2.5%, 5/199). Considering the high frequency of bacterial infections in our study, it seems that appropriate surveillance and control measures are essential to prevent the emergence and transmission of bacterial pathogens in rainbow trout farms.

Yersinia ruckeri —A threat not only to rainbow trout

Yersinia ruckeri (Y. ruckeri) can cause mortalities that are contributing to substantial economic losses in the rainbow trout (Oncorhynchus mykiss) aquaculture sector. Because of its most characteristic clinical signs, the disease in rainbow trout caused by this pathogen is called enteric redmouth disease. Although it is considered to affect mainly salmonids, there are reports in the available literature of isolating this bacterium from other fish species, both clinically healthy and diseased. The aim of this study was to analyse the available data concerning yersiniosis in non‐salmonid fish. The analysed data indicate that Y. ruckeri is a threat not only to rainbow trout. Some of the affected species have high commercial importance and mortalities may contribute to high economic losses. The disease symptoms may not be specific and can be different from those characteristic for enteric redmouth in trout, which may lead to misdiagnosis. Collected information indicates that infection with Y. ruckeri should be taken into account in the diagnostic procedures not only in salmonids.

Variations of the intestinal gut microbiota of farmed rainbow trout, Oncorhynchus mykiss (Walbaum), depending on the infection status of the fish.

The aim of the present study was to investigate the composition of the intestinal microbiota during the acute stage of a bacterial infection to understand how dysbiosis of the gut may influence overall taxonomic hierarchy and diversity, and determine if there exists a bacterial taxon(s) that serve as markers for healthy or diseased rainbow trout (Oncorhynchus mykiss). From July to September 2015, 29 specimens of 3-year-old (an average weight from 240·9±37·7 to 850·7±70·1g) rainbow trout O. mykiss were studied. Next-generation high-throughput sequencing of the 16S ribosomal RNA genes was applied to stomach and intestinal samples to compare the impact of infection status on the microbiota of rainbow trout O. mykiss (Walbaum) from the northwest part of Eurasia (Karelian region, Russia). The alpha diversity (Chao1, Simpson and Shannon index) of the microbial community of healthy rainbow trout was significantly higher than in unhealthy fish. The greatest contribution to the gut microbial composition of healthy fish was made by OTU's belonging to Bacillus, Serratia, Pseudomonas, Cetobacterium and Lactobacillus. Microbiota of unhealthy fish in most cases was represented by the genera Serratia, Bacillus and Pseudomonas. In microbiota of unhealthy fish there were also registered unique taxa such as bacteria from the family Mycoplasmataceae and Renibacterium. Analysis of similarities test revealed the significant dissimilarity between the microbiota of stomach and intestine (P≤0·05). A substantial finding was the absence of differences between microbial communities of the stomach and intestine in the unhealthy groups if compared with healthy fish. These results demonstrated alterations of the gut microbiota of farmed rainbow trout, O. mykiss during co-infections and can be useful for the development of new strategies for disease control programs.

Identification of some health indicators related to OIE notifiable viral diseases in Rainbow trout (Oncorhynchus mykiss) based on the strategic plan for producing Specific Pathogen Free (SPF) broodstock in Iran

Identification of some health indicators related to OIE notifiable viral diseases in Rainbow trout (Oncorhynchus mykiss) based on the strategic plan for producing Specific Pathogen Free (SPF) broodstock in Iran

The Isolation of Lactococcus garvieae from Eyes of Diseased Rainbow Trout (Oncorhynchus mykiss) with Exopthalmia

In this study, fish were sampled from 9 different fish farms in the dam lakes in the Eastern Black Sea Region between January 2016 and September 2018. It was isolated twenty-two bacteria isolates from eyes of diseased rainbow trout (Oncorhynchus mykiss). All isolates identification was carried out by using conventional biochemical tests, api 20 strep tests and PCR tests. ATCC 43921 reference strain was used as a positive control. According to results of the api 20 strep test, it was determined that 20 isolates from 22 bacterial isolates were Lactococcus garvieae. The PZR test was confirmed by using the pLG-1 and pLG-2 reference genes (16S rRNA) specific for the L. garvieae species. As a result of the study, it was confirmed that there were 20 L. garvieae from 22 strains isolated from rainbow trout in the dam lakes fish farms. The antibiotic susceptibility test results showed that L. garvieae isolates were resistant %100 to streptomycin, sulfamethoxazole and sulfamethoxazole+trimethoprim, 94.2% to ampicillin, 72.5% to oxytetracycline, 55.07% to erythromycin and 43.5% to oxolinic acid, 26.09% to enrofloxacin, % 20.3 doxycycline, 8,7% to amoxicillin and florphenicol. The most effective antibiotic was found to be florfenicol, amoxicillin, doxisicline and enrofloxacin.

Piscine orthoreovirus subtype 3 (PRV-3) causes heart inflammation in rainbow trout (Oncorhynchus mykiss)

Piscine orthoreovirus (PRV) mediated diseases have emerged throughout salmonid aquaculture. Three PRV subtypes are currently reported as causative agents of or in association with diseases in different salmonid species. PRV-1 causes heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar) and is associated with jaundice syndrome in farmed chinook salmon (Oncorhynchus tshawytscha). PRV-2 causes erythrocytic inclusion body syndrome (EIBS) in coho salmon in Japan. PRV-3 has recently been associated with a disease in rainbow trout (Oncorhynchus mykiss) characterized by anaemia, heart and red muscle pathology; to jaundice syndrome in coho salmon (Oncorhynchus kisutch). In this study, we conducted a 10-week long experimental infection trial in rainbow trout with purified PRV-3 particles to assess the causal relationship between the virus and development of heart inflammation. The monitoring the PRV-3 load in heart and spleen by RT-qPCR shows a progressive increase of viral RNA to a peak, followed by clearance without a measurable change in haematocrit. The development of characteristic cardiac histopathological findings occurred in the late phase of the trial and was associated with increased expression of CD8+, indicating cytotoxic T cell proliferation. The findings indicate that, under these experimental conditions, PRV-3 infection in rainbow trout act similarly to PRV-1 infection in Atlantic salmon with regards to immunological responses and development of heart pathology, but not in the ability to establish a persistent infection.

Diagnosis of Vibrio anguillarum in Cultured Rainbow Trout (Oncorhynchus mykiss) by Different Methods

DOI : 10.26650/EuroJBiol.2018.404499 Objective : In this study, the diagnosis of infection caused by Vibrio anguillarum in cultured rainbow trout (Oncorhynchus mykiss), in Turkey using bacteriological, histopathological and immunohistochemical methods was attempted. Materials and Methods : 15 rainbow trout samples showing signs of disease were investigated using bacteriological and histopatological methods. Results : Because of physiological and biochemical characteristics of bacteria growing on the medium, these bacteria were isolated and identified as V. anguillarum. As a result of the histopathologic examination of the tissues of diseased rainbow trout, hyperemia in the liver, degeneration of the epithelium of kidney tubules and necrosis in the interstitial area, enlargement in the gill filaments, cells having picnotic nucleus and several necrotic areas in the spleen were observed. It was also detected in the streptavidin-biotin staining method that the causative agent accumulates in the liver, spleen, kidney and also in the gills especially in the areas near around the blood vessels depending on the development stage of the disease. Conclusion : As a result, an immunoenzimatic method, streptavidin-biotin staining method was used in this study for the detection of the presence of V. anguillarum in the infected rainbow trout tissues.

Effects of fish size and route of infection on virulence of a Danish Yersinia ruckeri O1 biotype 2 strain in rainbow trout (Oncorhynchus mykiss)

The comparative virulence of Yersinia ruckeri serotype O1 biotype 2 strain 07111224 from a Danish outbreak of enteric redmouth disease in rainbow trout (Oncorhynchus mykiss) was investigated in different sizes of rainbow trout (5, 19, 25 and 52 g) using a panel of challenge methods (bath, intraperitoneal (IP) injection, anal intubation and cohabitation).The results show that Y. ruckeri 07111224 is virulent enough to successfully cause mortality in 5–52 g rainbow trout through three different infection routes (bath, IP injection and anal intubation), and strongly suggests that susceptibility to Y. ruckeri infection is dependent on fish size. Bath challenge (108 CFU/ml) caused 79% mortality in 5 g fish, while the mortality in 19–52 g fish was approximately 26%. IP injection challenges (105–106 CFU/individual) resulted in high mortalites in fish of all sizes. Anal intubation challenges (109 CFU/individual) induced 82% mortality in 5 g fish and decreased with increasing fish weight. Finally, cohabitation challenges induced 45% mortality in 5 g test fish when test fish were cohabitated 1:1 with shedder fish, while mortalities in test fish of five other challenge groups were lower (5–25%). Statistical models were fit to the data from each challenge model. The model parameter predictions suggests statistically significant effects of fish weight for bath, IP and anal intubation challenges. Furthermore, they highlight the importance of the ratio of shedders to test fish in cohabitation challenges and of the challenge doses, in particular for the IP challenge model.

Designing an in‐house ELISA to detect antibody against viral haemorrhagic septicaemia virus using recombinant N protein in Iranian farmed rainbow trout ( Oncorhynchus mykiss )

Viral haemorrhagic septicaemia (VHS) is one of the most important viral diseases in rainbow trout that has caused great losses to Iranian rainbow trout aquaculture industry in the last 3 years. Therefore, rapid and reliable diagnosis of VHS virus infections is of great importance. An enzyme linked immunosorbent assay (ELISA) method was performed to study serum antibodies against viral haemorrhagic septicaemia virus (VHSV) using recombinant fragments of their N protein. For this purpose, the virus was first isolated from an infected farm. A part of the nucleocapsid (1–505 bp) gene was amplified by RT-PCR using specific primers. The amplified fragment was ligated to pMALc2x vector and transferred to DH5α strain of Escherichia coli. Then, recombinant plasmids were tested for protein expression in E. coli Rosetta strain. SDS-PAGE analysis indicated the production of a recombinant protein with an expected molecular weight of 61 KDa. Analysis of trout serum samples from seven previously infected farms and two VHS free farms showed that the designed ELISA method was effective in diagnosing the infected fish. The results revealed that the developed serological assay using designed ELISA based on recombinant protein (N) has the potential to be used in monitoring studies and to determine the prevalence of VHS in rainbow trout farms. The present data allow evaluating the levels of nonneutralizing antibodies without crude virus preparations.

Wild fish are negligible transmitters of viral haemorrhagic septicaemia virus (VHSV) genotype Id in the VHS restriction zone in Finland.

Wild fish were suspected to be the source of reinfection by viral haemorrhagic septicaemia virus (VHSV) in Finnish brackish water rainbow trout farms located in a restriction zone regarding viral haemorrhagic septicaemia (VHS) comprising the entire Province of Åland, Baltic Sea, in the 2000s. Altogether, 1636 wild fish of 17 different species living in the vicinity of infected fish farms were screened for VHSV during the years 2005-2008. Additionally, 2 uninfected wild fish species as well as farmed whitefish were introduced into a VHS-positive fish farm to test whether they became infected by VHSV from the clinically diseased rainbow trout. Wild fish did not test positive for VHSV on any occasion. In contrast, whitefish introduced to a VHS-positive farm were infected with VHSV genotype Id and started to replicate the virus for a short time during the trial. Whitefish are farmed together with, or in the vicinity of, farmed rainbow trout in the study area and, according to this study, are a possible source of the recurring infection in the restriction area. A sprivivirus was isolated from all fish species in the infection trial without causing mortality in the test groups.

Isolation characterization, virulence potential of Weissella ceti responsible for weissellosis outbreak in rainbow trout (Oncorhynchus mykiss) cultured in Mexico.

Weissella ceti, a Gram-positive nonmotile bacterium, is currently an emerging pathogen within rainbow trout (Oncorhynchus mykiss) farms in China, Brazil, the United States, and Japan. This study is the first to isolate, identify, and characterize W.ceti isolates from rainbow trout farmed in Mexico. In late 2015, a severe disease outbreak caused a 60% mortality rate among 20,000 fish. The diseased rainbow trout (100-300g average) exhibited severe cachexia, body darkening, abdominal distension, exophthalmia, haemorrhages, and corneal opacity. Internally, diseased fish had pale gills; multifocal, disseminated whitish spots on the liver; haemorrhages in the swim bladder, ovary, and on the parietal surface of the muscle; and hearts with pseudo-membrane formation. Histologically, lesions were characterized by corneal oedema, degenerative and necrotic hepatitis, and meningitis. A brain (W-1) and kidney (W-2) isolate were identified as W.ceti through polyphasic taxonomy, which included phenotypic characterization and 16S rRNA sequencing. RAPD and ERIC-PCR analyses demonstrated genetic homogeneity among the Mexican isolates. Virulence tests in rainbow trout through intraperitoneal W.ceti injections at concentrations of 1×104 , 1×105 , and 1×106 CFU per fish resulted in cumulative mortality rates of 25%, 62.5%, and 87.5%, respectively, as well as the same clinical signs of hemorrhagic septicaemia as were recorded for the natural outbreak. The present report is the first to confirm the presence of W.ceti in Mexico, thus extending the known geographical distribution of this pathogen across the Americas.

Retrospective Evaluation of Marker-Assisted Selection for Resistance to Bacterial Cold Water Disease in Three Generations of a Commercial Rainbow Trout Breeding Population.

Bacterial cold water disease (BCWD), caused by Flavobacterium psychrophilum, is an endemic and problematic disease in rainbow trout (Oncorhynchus mykiss) aquaculture. Previously, we have identified SNPs (single nucleotide polymorphisms) associated with BCWD resistance in rainbow trout. The objectives of this study were (1) to validate the SNPs associated with BCWD resistance in a commercial breeding population; and (2) to evaluate retrospectively the accuracy of MAS (marker-assisted selection) for BCWD resistance in this commercial breeding program. Three consecutive generations of the Troutlodge May breeding population were evaluated for BCWD resistance. Based on our previous studies, a panel of 96 SNPs was selected and used to genotype the parents and ten offspring from each of the 138 full-sib families of the 2015 generation, and 37 SNPs associated with BCWD resistance were validated. Thirty-six of the validated SNPs were clustered on chromosomes Omy3, Omy8 and Omy25. Thus, at least three QTL (quantitative trait loci) for BCWD resistance were validated in the 2015 generation. Three SNPs from each QTL region were used for haplotype association analysis. Three haplotypes, Omy3TGG, Omy8GCG and Omy25CGG, were found to be associated with BCWD resistance in the 2015 generation. Retrospective analyses were then performed to evaluate the accuracy of MAS for BCWD resistance using these three favorable haplotypes. The accuracy of MAS was estimated with the Pearson correlation coefficient between the total number of favorable haplotypes in the two parents and the family BCWD survival rates. The Omy8 and Omy25 haplotypes were positively correlated with the family BCWD survival rates across all three generations. The accuracies of MAS using these two haplotypes together were consistently around 0.5, which was equal or greater than the accuracy of the conventional family-based selection in the same generation. In conclusion, we have demonstrated that MAS for BCWD resistance is feasible in this commercial rainbow trout breeding population.

Dysregulation of B Cell Activity During Proliferative Kidney Disease in Rainbow Trout.

Proliferative kidney disease (PKD) is a widespread disease caused by the endoparasite Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea). Clinical disease, provoked by the proliferation of extrasporogonic parasite stages, is characterized by a chronic kidney pathology with underlying transcriptional changes indicative of altered B cell responses and dysregulated T-helper cell-like activities. Despite the relevance of PKD to European and North American salmonid aquaculture, no studies, to date, have focused on further characterizing the B cell response during the course of this disease. Thus, in this work, we have studied the behavior of diverse B cell populations in rainbow trout (Oncorhynchus mykiss) naturally infected with T. bryosalmonae at different stages of preclinical and clinical disease. Our results show a clear upregulation of all trout immunoglobulins (Igs) (IgM, IgD, and IgT) demonstrated by immunohistochemistry and Western blot analysis, suggesting the alteration of diverse B cell populations that coexist in the infected kidney. Substantial changes in IgM, IgD, and IgT repertoires were also identified throughout the course of the disease further pointing to the involvement of the three Igs in PKD through what appear to be independently regulated mechanisms. Thus, our results provide strong evidence of the involvement of IgD in the humoral response to a specific pathogen for the first time in teleosts. Nevertheless, it was IgT, a fish-specific Ig isotype thought to be specialized in mucosal immunity, which seemed to play a prevailing role in the kidney response to T. bryosalmonae. We found that IgT was the main Ig coating extrasporogonic parasite stages, IgT+ B cells were the main B cell subset that proliferated in the kidney with increasing kidney pathology, and IgT was the Ig for which more significant changes in repertoire were detected. Hence, although our results demonstrate a profound dysregulation of different B cell subsets during PKD, they point to a major involvement of IgT in the immune response to the parasite. These results provide further insights into the pathology of PKD that may facilitate the future development of control strategies.

Antimicrobial resistance and molecular characterization of Pantoea agglomerans isolated from rainbow trout (Oncorhynchus mykiss) fry

Aquaculture has become an important candidate as an animal protein source through its growth over the last decade. Based upon a report from the Food and Agriculture Organization of the United Nations, it is the fastest growing sector of the food industry, yet the pathogenicity of many biological agents involved in aquaculture is still unknown. In this study, we isolated Pantoe agglomerans from diseased rainbow trout on several occasions and also attempted to determine their phenotypic and genotypic characteristics, including antimicrobial resistance, of four bacterial isolates.In the present study, P. agglomerans was isolated from diseased rainbow trout as a pathogenic agent. The identification of the P. agglomerans isolates from the rainbow trout was performed through biochemical tests and 16S rRNA sequence analysis. These isolates were predominately biochemically homogeneous, although some features were different, such as seen in methyl-red, mannose and lipase activity tests. All four studied isolates were identified as 99% identical to P. agglomerans based on sequence analysis. The isolates were compared through a phylogenetic analysis with P. agglomerans sequences recovered from 16 other countries and accessed from the GenBank database. All isolates in our study were at least 98.2% similar to sequences from GenBank.Furthermore, the phenotypic antimicrobial susceptibility of the isolates in this study was analyzed through both disc diffusion and broth micro dilution minimum inhibitory concentration (MIC) tests. Although there were some differences between two phenotypic antimicrobial tests, all studied isolates were found susceptible to different antimicrobials. In addition genotypic antimicrobial resistance characteristics were assessed by the presence of antimicrobial resistance genes (ARGs), in which qnrS and sul2 were detected for the first time in P. agglomerans.

Salmonid Alphavirus (SAV).

Salmonid alphavirus (SAV), genus Alphavirus, family Togaviridae, is a single-stranded RNA virus affecting Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). It is known to be responsible for pancreas disease (PD) and sleeping disease (SD) which are increasing problems, causing high fish mortality and economic losses in the European aquaculture industry. Pancreas disease was first described in Atlantic salmon in Scotland in 1976 and a similar disease caused by the closely related sleeping disease virus was first described in rainbow trout in France. There have also been reports of salmonid alphavirus infections from other European countries, including Ireland, England, Norway, Germany, Italy, and Spain. Salmonid alphaviruses have been classified into six subtypes (SAV1–6). SAV1 and SAV4–6 cause pancreas disease in Atlantic salmon in Ireland or Scotland, SAV2 is the causative agent of sleeping disease in rainbow trout, and SAV3 has been detected in Atlantic salmon in Norway. The aim of this paper was to summarise current knowledge of infections caused by salmonid alphavirus and diagnostic methods including the newest techniques, and to briefly describe prevention from SAV infections by vaccination.

A lytic bacteriophage of the newly emerging rainbow trout pathogen Weissella ceti

This study was conducted to isolate and characterize a bacteriophage of a newly emerging pathogen, Weissella ceti, which causes weissellosis outbreaks of intensively farmed rainbow trout worldwide. The phage appeared together with the cultured Weissella ceti during isolation of pathogen from kidney of diseased rainbow trout. The morphological, physiological, proteomic and lytic spectrum were characterized. This phage, named PWc, belonged to the family Siphoviridae and possessed an isometric head (approximately 65 nm in diameter) and a flexible, non-contractile tail of 170–180 nm in length. The latent time and burst size of PWc were approximately 25 min and 16 PFU/infected cells, respectively. The PWc was relatively stable over a wide range of temperatures and pH values and possessed a broad lytic spectrum, lysing all 36 tested W. ceti strains isolated from diseased rainbow trout in Japan. The protein profile of the phage was obtained using SDS-PAGE analysis, and the potential packaging strategy was determined based on terminase large subunit sequence analysis. This is the first study to investigate a lytic bacteriophage of a newly emerging pathogen W. ceti that causes infectious disease in rainbow trout.