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Systemic granuloma observed in Atlantic salmon Salmo salar raised to market size in a freshwater recirculation aquaculture system

Christopher Good, David P. Marancik, Timothy J. Welch, Travis May, John Davidson, Steven Summerfelt
Aquaculture research 2015 pp. 1-5
Salmo salar, adipose tissue, adults, blood chemistry, brain, calcification, disease prevalence, fish, fish culture, fish diseases, freshwater, granuloma, harvesting, histopathology, liver, marketing, metastasis, microbial culture, polymerase chain reaction, recirculating aquaculture systems, skeletal muscle, staining
Systemic granuloma was observed in sampled adult Atlantic salmon Salmo salar raised to harvest size in a freshwater recirculation aquaculture system. The prevalence of this condition was estimated at 10-20% of the population, with affected individuals grossly demonstrating pathology in varying degrees of extent and severity. Six downgraded fish were sampled at final harvest, and the following assessments were carried out: gross pathology and histopathology, bacterial culture and 16S PCR, and plasma chemistry. Granulomas were observed in all tissues examined, including brain and skeletal muscle; the most extensively affected tissues were liver and visceral adipose tissue. Special staining (Von Kossa) revealed a central core of mineral and/or necrotic debris in the granulomas. Culture and PCR did not reveal the presence of an agent or agents associated with this condition; likewise, plasma chemistry results were unremarkable. Overall, it is likely that the observed pathologies were related to mineral imbalance leading to widespread metastatic calcification; however, the true causation of the observed pathologies remains unknown, and further research needs to be conducted to complete our understanding. To our knowledge, this is the first description of systemic granuloma in Atlantic salmon.