Search

ABSTRACT Recirculating Aquaculture Systems (RAS) have been proposed as the future of aquaculture, because they can be used anywhere regardless of access to water, they offer high level of control over farming environment, including biosecurity, and are considered to be sustainable. However, despite of continuous development, there can be still issues with water quality affecting gill health of fish farmed in these systems. This review provides an overview of fish gill structure and gill immune response, and discusses the known impacts of RAS on gill health. Several experimental studies have inadequately reported conditions, particularly water quality, making it difficult to determine if the observed effects were due to water quality issues or RAS system itself. It is crucial for studies investigating the impact of RAS on fish to report water quality during the study. Furthermore, assessments of RAS effects on gill health should include sufficient independent replicates and flow through controls using a common water source. Various methods have been used to assess gill health in RAS, including gill histology, presence of pathogens, gene expression in the gills and gill microbiome analysis. Differences in gill health in fish from RAS and a flow through system have been shown for a number of freshwater and marine fish species. However, these results have been inconsistent across studies, and some results have been challenging to interpret as indicators of gill health. Holistic studies including a number of different methods to assess fish gills would give more conclusive results. More research is needed, in particular, on brackish and marine RAS, to fully understand their impacts on gill health. [ABSTRACT FROM AUTHOR]

Melanized focal changes (MFCs) in the fillet of farmed Atlantic salmon is a major quality concern. The changes are thought to initially appear as acute red focal changes (RFCs) that progress into chronic MFCs. Recent findings have indicated that hypoxia may be important in their development, possibly leading to necrosis affecting not only myocytes but also adipocytes. Thus, the aim of this study was to investigate possible hypoxic conditions in RFCs and the subsequent inflammatory responses and lesions in the adipose tissue in RFCs and MFCs. A collection of RFCs, MFCs and control muscle samples from several groups of farmed salmon was studied. Using immunohistochemistry, we found induction of the hypoxia‐inducible factor 1 pathway in RFCs. Histological investigations of RFCs and MFCs revealed different stages of fat necrosis, including necrotic adipocytes, a myospherulosis‐like reaction and the formation of pseudocystic spaces. Accumulations of foamy macrophages were detected in MFCs, indicating degradation and phagocytosis of lipids. Using in situ hybridization, we showed the presence of tyrosinase‐ and tyrosinase‐related protein‐1‐expressing amelanotic cells in RFCs, which in turn became melanized in MFCs. In conclusion, we propose a sequence of events leading to the formation of MFCs, highlighting the pivotal role of adiposity, hypoxia and fat necrosis. [ABSTRACT FROM AUTHOR]

Cardiomyopathy syndrome (CMS) poses a significant threat to farmed Atlantic salmon (Salmo salar), leading to high mortality rates during the seawater phase. Given that controlled experimental challenge trials with PMCV do not reproduce the mortality observed in severe field outbreaks of CMS, field trials on natural CMS outbreaks are warranted. This field study explored the impact of a clinical nutrition intervention, specifically a diet enriched with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on a severe CMS outbreak in a commercial sea farm. CMS was diagnosed in a single sea cage with high mortality rates. Histopathological analysis, RT-qPCR in situ hybridization for virus detection, and fatty acid composition analysis were used to monitor the impact of disease and the inclusion of EPA and DHA in heart tissue. Following the implementation of clinical nutrition, a decline in mortality rates, regression of CMS-associated changes, and a significant reduction in piscine myocarditis virus (PMCV) RNA load were observed within the salmon population. Fatty acid composition analysis of heart samples demonstrated increased levels of EPA and DHA, reinforcing the association between dietary factors, viral load dynamics, and overall fish health. Although further validation is needed in future studies, as field trials may not be sufficient to establish causation, our results indicate that optimizing the EPA + DHA levels may prove beneficial in severe CMS outbreaks. [ABSTRACT FROM AUTHOR]

Canine hemangiosarcoma (HSA) is a highly malignant tumor derived from hematopoietic stem cells and commonly occurs in visceral organs or skin. Visceral HSAs are particularly aggressive and progress rapidly despite multimodal treatment. Tumor-associated macrophages (TAMs) play a central role in carcinogenesis, tumor progression, and metastasis in humans and murine models. In this retrospective study, we investigated the prevalence and phenotype of TAMs in privately owned, treatment-naïve dogs with naturally occurring HSA. We used CD204 as a general macrophage marker and CD206 as a marker for M2-polarized macrophages. Formalin-fixed paraffin-embedded tissues from HSAs in the spleen (n = 9), heart (n = 6), and other locations (n = 12) from 17 dogs were sectioned and immunohistochemically labeled with CD204 and CD206 antibodies. The mean number of log(CD204)- and log(CD206)-positive cells and the ratio of log(CD206/CD204)-positive cells were compared with normal surrounding tissues and between tumor locations. There were significantly more macrophages and M2 macrophages, and a higher ratio of M2 macrophages to total macrophages in tumor hot spots (P =.0002, P <.0001, and P =.0002, respectively) and in tumor tissues outside of hot spots (P =.009, P =.002, and P =.007, respectively) than in normal surrounding tissues. There were no significant differences between tumor locations, but there was a trend toward higher numbers of CD204-positive macrophages within the splenic tumors. There was no association between histological parameters or clinical stage and TAM numbers or phenotype. As in humans, TAMs in dogs with HSA have a predominantly M2-skewed phenotype. Dogs with HSA could serve as excellent models to evaluate new TAM-reprogramming therapies. [ABSTRACT FROM AUTHOR]

Simple Summary: IgT is a specific type of antibody found in teleost fish that is crucial for protecting mucosal surfaces. However, studying IgT is challenging due to the limited available cell markers. Here, we investigated the distribution of IgT mRNA+ cells and pIgR mRNA+ cells (essential for Ig transport over cell membranes) in Atlantic salmon (Salmo salar) intestines. Using in situ hybridization, we examined two different sizes (developmental stages) of the fish and compared the hybridization-positive cell distribution between vaccinated and unvaccinated fish. Our findings revealed that IgT mRNA+ cells were mainly located beneath the intestinal mucosa, specifically in the lamina propria, while pIgR mRNA+ cells were found in both the lamina propria and mucosa. Additionally, vaccinated fish exhibited abdominal adhesions with tissue containing IgT and pIgR mRNA+ cells. We observed regional variations in the distribution of IgT mRNA+ cells within the salmon intestine that were unaffected by intraperitoneal vaccination but sensitive to fish age. This study provides new insights into the distribution and dynamics of IgT and pIgR mRNA+ cells, advancing our understanding of the spatial mucosal immune system and its implications for teleosts, with potential applications in aquaculture. The newly discovered IgT+ B cell is thought to play a dominant role in mucosal immunity, but limited studies have examined its distribution in fish species, hindering our understanding of its function. This study investigated IgT and poly Ig receptor (pIgR) mRNA+ cell distribution in Atlantic salmon (Salmo salar) gut using RNAscope in situ hybridization (ISH) and assessed the effects of vaccination. The pyloric caeca, mid-intestine (first and second parts), and posterior segment in two weight stages (Group 1: avg. 153 g, Group 2: avg. 1717 g) were examined in both vaccinated and unvaccinated fish. ISH revealed more IgT mRNA+ cells in the second part of the midgut compared to other intestinal segments, as well as a higher number of positive cells in Group 2 (older fish). In line with previous findings, intraperitoneal vaccination had no significant impact on the number of IgT+ transcripts. IgT mRNA+ cells were found mostly in the lamina propria and near capillaries, while pIgR was registered in both the lamina propria and mucosa. Interestingly, vaccinated fish presented adhesions and granulomatous tissue in the peritoneum, with both IgT and pIgR mRNA+ cells. Taken together, these results suggest that the distribution of IgT mRNA+ cells in the intestine of Atlantic salmon is region-specific and is not affected by intraperitoneal vaccination but varies with fish age. [ABSTRACT FROM AUTHOR]

Although statistical analysis of our material could indicate that PRV-1 infection is associated with red muscle melanization, other infections or even co-infections with SAV2 or PMCV may have contributed to the development of the condition. All affected samples were positive for PRV-1 with a median I C i SB t sb value of 30.2, for the control fish, four samples were PRV-1 positive, and two were negative. Keywords: filet; melanin; melano-macrophage; piscine myocarditis virus; piscine orthoreovirus 1; salmonid alphavirus EN filet melanin melano-macrophage piscine myocarditis virus piscine orthoreovirus 1 salmonid alphavirus 453 458 6 03/10/23 20230401 NES 230401 INTRODUCTION Farmed Atlantic salmon ( I Salmo salar i L.) are susceptible to melanization of the white muscle ("the filet"), where melanized spots have a prevalence of 20%-30% at slaughter (Mørkøre et al., [16]). Melanized focal changes in skeletal muscle in farmed Atlantic salmon after natural infection with Piscine orthoreovirus (PRV). [Extracted from the article]