Dataset Information

Histopathological investigation of complex gill disease in sea farmed Atlantic salmon.

ABSTRACT: Various agents including Ca. Piscichlamydia salmonis, Ca. Branchiomonas cysticola, Desmozoon lepeophtherii, Paramoeba perurans and salmon gill poxvirus may be associated with complex gill disease in Atlantic salmon. Co-infections involving two or more of these agents are common and histopathological interpretation of lesions is therefore challenging. In this study, we developed a semi-quantitative scoring system for examination of histopathological gill lesions in sea-farmed Atlantic salmon suffering from gill disease. Following qPCR analysis of gills sampled for Ca. P. salmonis, Ca. B. cysticola, D. lepeophtherii and P. perurans from 22 geographically spread outbreaks, five cases representing different infectious loads and combinations of agents were chosen for histopathological scoring. Twenty-eight histological features were evaluated and potential associations between individual pathological changes and the occurrence of individual agents studied. The inter-observer agreement in interpretation of histological parameters between the three pathologists involved, was calculated to validate robustness of the scoring scheme. Seventeen histological parameters met the criteria for inter-observer agreement analysis and were included in the calculation. The three most frequent findings were identification of subepithelial leukocytes, epithelial cell hyperplasia and mucus cell hyperplasia. While few findings could be specifically related to particular agents, necrosis in hyperplastic lesions, pustules and necrosis of subepithelial cells appeared to be associated with the presence of Ca. B. cysticola. Further, lesion profiles clearly support the previously identified association between P. perurans and pathological changes associated with AGD. Very few pathological changes were observed in the single case in which Ca. P. salmonis was the dominating agent. Some lesions were only very rarely observed e.g. chloride cell necrosis, epithelial cell apoptosis, lamellar deposition of melanin and haemophagocytosis. The scoring scheme developed and applied was robust and sensitive. A less extensive scheme for routine diagnostic use is proposed.

SUBMITTER: Gjessing MC

PROVIDER: S-EPMC6776330 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Histopathological investigation of complex gill disease in sea farmed Atlantic salmon.

Gjessing Mona C MC Steinum Terje T Olsen Anne Berit AB Lie Kai Inge KI Tavornpanich Saraya S Colquhoun Duncan J DJ Gjevre Anne-Gerd AG

PloS one 20191003 10

Various agents including Ca. Piscichlamydia salmonis, Ca. Branchiomonas cysticola, Desmozoon lepeophtherii, Paramoeba perurans and salmon gill poxvirus may be associated with complex gill disease in Atlantic salmon. Co-infections involving two or more of these agents are common and histopathological interpretation of lesions is therefore challenging. In this study, we developed a semi-quantitative scoring system for examination of histopathological gill lesions in sea-farmed Atlantic salmon suff ...[more]

PMID: 31581255

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Project description:The gill of teleost fish is a multifunctional organ involved in many physiological processes such as gas exchange, osmotic and ionic regulation, acid-base balance and excretion of nitrogenous waste. Due to its extensive interface with the environment, the gill plays a key role as a primary mucosal defense tissue against pathogens, as manifested by the presence of the gill-associated lymphoid tissue (GIALT). In recent years, the prevalence of multifactorial gill pathologies has increased significantly, causing substantial losses in Atlantic salmon aquaculture. The transition from healthy to unhealthy gill phenotypes and the progression of multifactorial gill pathologies, such as proliferative gill disease (PGD), proliferative gill inflammation (PGI) and complex gill disorder (CGD), are commonly characterized by epithelial hyperplasia, lamellar fusion and inflammation. Routine monitoring for PGD relies on visual inspection and non-invasive scoring of the gill tissue (gross morphology), coupled with histopathological examination of gill sections. To explore the underlying molecular events that are associated with the progression of PGD, we sampled Atlantic salmon from three different marine production sites in Scotland and examined the gill tissue at three different levels of organization: gross morphology with the use of PGD scores (macroscopic examination), whole transcriptome (gene expression by RNA-seq) and histopathology (microscopic examination). Our results strongly suggested that the changes in PGD scores of the gill tissue were not associated with the changes in gene expression or histopathology. In contrast, integration of the gill RNA-seq data with the gill histopathology enabled us to identify common gene expression patterns associated with multifactorial gill disease, independently from the origin of samples. We demonstrated that the gene expression patterns associated with multifactorial gill disease were dominated by two processes: a range of immune responses driven by pro-inflammatory cytokines and the events associated with tissue damage and repair, driven by caspases and angiogenin.

Project description:Understanding the relationship between resident microbiota and disease in cultured fish represents an important and emerging area of study. Marine gill disorders in particular are considered an important challenge to Atlantic salmon (Salmo salar) aquaculture, however relatively little is known regarding the role resident gill microbiota might play in providing protection from or potentiating different gill diseases. Here, 16S rRNA sequencing was used to examine the gill microbiome alongside fish health screening in farmed Atlantic salmon. Results were used to explore the relationship between microbial communities and gill disease. Microbial community restructuring was observed throughout the sampling period and linked to varied drivers of change, including environmental conditions and severity of gill pathology. Taxa with significantly greater relative abundance on healthier gills included isolates within genus Shewanella, and taxa within family Procabacteriaceae. In contrast, altered abundance of Candidatus Branchiomonas and Rubritalea spp. were associated with damaged gills. Interestingly, more general changes in community richness and diversity were not associated with altered gill health, and thus not apparently deleterious to fish. Gross and histological gill scoring demonstrated seasonal shifts in gill pathology, with increased severity of gill damage in autumn. Specific infectious causes that contributed to observed pathology within the population included the gill disorder amoebic gill disease (AGD), however due to the uncontrolled nature of this study and likely mixed contribution of various causes of gill disease to observed pathology results do not strongly support an association between the microbial community and specific infectious or non-infectious drivers of gill pathology. Results suggest that the microbial community of farmed Atlantic salmon gills undergo continual restructuring in the marine environment, with mixed influences upon this change including environmental, host, and pathogenic factors. A significant association of specific taxa with different gill health states suggests these taxa might make meaningful indicators of gill health. Further research with more frequent sampling and deliberate manipulation of gills would provide important advancement of knowledge in this area. Overall, although much is still to be learnt regarding what constitutes a healthy or maladapted gill microbial community, the results of this study provide clear advancement of the field, providing new insight into the microbial community structure of gills during an annual production cycle of marine-stage farmed Atlantic salmon.

Project description:BackgroundSea lice have significant negative economic and welfare impacts on marine Atlantic salmon farming. Since host resistance to sea lice has a substantial genetic component, selective breeding can contribute to control of lice. Genomic selection uses genome-wide marker information to predict breeding values, and can achieve markedly higher accuracy than pedigree-based methods. Our aim was to assess the genetic architecture of host resistance to sea lice, and test the utility of genomic prediction of breeding values. Individual lice counts were measured in challenge experiments using two large Atlantic salmon post-smolt populations from a commercial breeding programme, which had genotypes for ~33 K single nucleotide polymorphisms (SNPs). The specific objectives were to: (i) estimate the heritability of host resistance; (ii) assess its genetic architecture by performing a genome-wide association study (GWAS); (iii) assess the accuracy of predicted breeding values using varying SNP densities (0.5 to 33 K) and compare it to that of pedigree-based prediction; and (iv) evaluate the accuracy of prediction in closely and distantly related animals.ResultsHeritability of host resistance was significant (0.22 to 0.33) in both populations using either pedigree or genomic relationship matrices. The GWAS suggested that lice resistance is a polygenic trait, and no genome-wide significant quantitative trait loci were identified. Based on cross-validation analysis, genomic predictions were more accurate than pedigree-based predictions for both populations. Although prediction accuracies were highest when closely-related animals were used in the training and validation sets, the benefit of having genomic-versus pedigree-based predictions within a population increased as the relationships between training and validation sets decreased. Prediction accuracy reached an asymptote with a SNP density of ~5 K within populations, although higher SNP density was advantageous for cross-population prediction.ConclusionsHost resistance to sea lice in farmed Atlantic salmon has a significant genetic component. Phenotypes relating to host resistance can be predicted with moderate to high accuracy within populations, with a major advantage of genomic over pedigree-based methods, even at relatively sparse SNP densities. Prediction accuracies across populations were low, but improved with higher marker densities. Genomic selection can contribute to lice control in salmon farming.

Dataset Information

Histopathological investigation of complex gill disease in sea farmed Atlantic salmon.

Publications

Histopathological investigation of complex gill disease in sea farmed Atlantic salmon.

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