Abstract
Haemorrhagic smolt syndrome (HSS) is a disorder of unknown aetiology causing losses in the fresh water phase of Atlantic salmon farming. Normally, the mortality is limited and symptoms disappear upon seawater exposure. In this case study, classical HSS pathology with internal organ haemorrhages and nephrocalcinosis was diagnosed, and the losses were substantial. Microarray analyses of head kidney revealed association between HSS and enhanced expression of stress genes and proteins reducing bioavailability of iron, heme, and retinol. In parallel, suppression of multiple metabolic pathways was observed. Up-regulation of genes encoding acute phase proteins, complement, and lectins indicated mild inflammation but without characteristic features of viral or bacterial infections. Microarray analyses highlighted several members of tumor necrosis factor receptor superfamily that may control development of B-cell immunity. Examination of IgM at the mRNA and protein levels showed the impact of HSS on vaccine responses. In fish without HSS symptoms (non-HSS), titres of vaccine specific antibodies to A-layer of Aeromonas salmonicida subsp. salmonicida and Moritella viscosa and antibodies binding to DNP-keyhole limpet hemocyanin (DNP-KLH), which are presumably polyreactive, were respectively four- and 14-fold higher than in HSS-diseased fish. Parallel sequencing of variable regions of immunoglobulin Mrevealed a larger size of most abundant clonotypes shared by multiple individuals in the non-HSS group. The results of the current case study indicated that, in addition to direct damage, HSS suppresses humoral immune responses including the production of specific and polyreactive antibodies.
Highlights
Haemorrhagic smolt syndrome (HSS) was first detected in Scotland in 1996 [1] and today fish with the clinical signs of HSS are repeatedly found in Norway [2]
No other diagnosis was found by clinical examination and histopathology, and repeated PCR-testing for Piscine orthoreovirus (PRV) and infectious pancreatic necrosis virus (IPNV), due to historical outbreaks at the farm, was negative
Expression differences between HSS-affected and healthy control salmon were shown by 542 genes, of which 327 genes (60.3%) had lower expression in HSS fish
Summary
Haemorrhagic smolt syndrome (HSS) was first detected in Scotland in 1996 [1] and today fish with the clinical signs of HSS are repeatedly found in Norway [2]. Salmon suffering from HSS are characterized by pale gills and yellow liver, bleeding at the fin bases, low haematocrit, multiple haemorrhage in organs and endothelial tissue, and renal pathology. Biology 2020, 9, 1 usually low and HSS does not affect the growth of fish. The disease has been linked to osmoregulatory challenges associated with the process of smoltification and has commonly been observed in the late phase of the freshwater period. To this end, no association between HSS and infectious agents has been shown, and diagnostic tests have not detected any known pathogens. Nylund and co-workers found evidence of two types of virus-like particles in different tissues and cell types by electron microscopy [2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
