Differentiating salient histopathologic changes from normal anatomic features or tissue artifacts can be decidedly challenging, especially for the novice fish pathologist. As a consequence, findings of questionable accuracy may be reported inadvertently, and the potential negative impacts of publishing inaccurate histopathologic interpretations are not always fully appreciated. The objectives of this article are to illustrate a number of specific morphologic findings in commonly examined fish tissues (e.g., gills, liver, kidney, and gonads) that are frequently either misdiagnosed or underdiagnosed, and to address related issues involving the interpretation of histopathologic data. To enhance the utility of this article as a guide, photomicrographs of normal and abnormal specimens are presented. General recommendations for generating and publishing results from histopathology studies are additionally provided. It is hoped that the furnished information will be a useful resource for manuscript generation, by helping authors, reviewers, and readers to critically assess fish histopathologic data.
The consequences of high (735 copepodids fish ) level exposures of size-matched juvenile pink and chum salmon to Lepeophtheirus salmonis copepodids were examined. At both levels of exposure the prevalence and abundance of L. salmonis was significantly higher on chum salmon. In addition, the weight of exposed chum salmon following the high exposure was significantly less than that of unexposed chum salmon. At both exposures, the haematocrit of exposed chum salmon was significantly less than that of unexposed chum. Neither weight nor haematocrit of pink salmon was affected by exposures at these levels. Despite the presence of microscopic inflammatory lesions associated with attachment of L. salmonis on the epithelium of gill and fin of both salmon species, there were no mortalities following either exposure. A transient cortisol response was observed in chum salmon 21 d after low exposure. An earlier and quantitatively higher expression of the proinflammatory genes interleukin-8 (IL-8), tumour necrosis factor α-1 (TNFα-1) and interleukin-1β (IL-1β) in fin and head kidney of pink salmon suggested a mechanism of more rapid louse rejection in this species. Together, these observations indicate a relatively enhanced innate resistance to L. salmonis in the juvenile pink salmon compared with the juvenile chum salmon.
Background: Infectious salmon anaemia (ISA) is a viral disease of marine-farmed Atlantic salmon (Salmo salar) caused by ISA virus (ISAV), which belongs to the genus Isavirus, family Orthomyxoviridae. The virus is considered to be carried by marine wild fish and for over 25 years has caused major disease outbreaks in marine-farmed Atlantic salmon in the Northern hemisphere. In the Southern hemisphere, ISAV was first detected in Chile in 1999 in marine-farmed Coho salmon (Oncorhynchus kisutch). In contrast to the classical presentation of ISA in Atlantic salmon, the presence of ISAV in Chile until now has only been associated with a clinical condition called Icterus Syndrome in Coho salmon and virus isolation has not always been possible. During the winter of 2007, unexplained mortalities were registered in market-size Atlantic salmon in a grow-out site located in Chiloé in Region X of Chile. We report here the diagnostic findings of the first significant clinical outbreak of ISA in marine-farmed Atlantic salmon in Chile and the first characterization of the ISAV isolated from the affected fish.
Background: Infectious salmon anaemia (ISA) virus (ISAV), which causes ISA in marine-farmed Atlantic salmon, is an orthomyxovirus belonging to the genus Isavirus, family Orthomyxoviridae. ISAV agglutinates erythrocytes of several fish species and it is generally accepted that the ISAV receptor destroying enzyme dissolves this haemagglutination except for Atlantic salmon erythrocytes. Recent work indicates that ISAV isolates that are able to elute from Atlantic salmon erythrocytes cause low mortality in challenge experiments using Atlantic salmon. Previous work on ISAVinduced haemagglutination using the highly pathogenic ISAV strain NBISA01 and the low pathogenic ISAV strain RPC/NB-04-0851, showed endocytosis of NBISA01 but not RPC/NB-04-0851. Realtime RT-PCR was used to assess the viral RNA levels in the ISAV-induced haemagglutination reaction samples, and we observed a slight increase in viral RNA transcripts by 36 hours in the haemagglutination reaction with NBISA01 virus when the experiment was terminated. However, a longer sampling interval was considered necessary to confirm ISAV replication in fish erythrocytes and to determine if the infected cells mounted any innate immune response. This study examined the possible ISAV replication and Type I interferon (IFN) system gene induction in Atlantic salmon erythrocytes following ISAV haemagglutination.
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