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

Authors: GOOD, CHRISTOPHER - Freshwater Institute; Marancik, David; Welch, Timothy - Tim; MAY, TRAVIS - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; SUMMERFELT, STEVEN - Freshwater Institute

Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2015
Publication Date: 5/16/2015
Publication URL: https://handle.nal.usda.gov/10113/61041
Citation: Good, C., Marancik, D.P., Welch, T.J., May, T., Davidson, J., Summerfelt, S. 2015. Systemic granuloma observed in Atlantic salmon Salmo salar raised to market size in a freshwater recirculation aquaculture system. Aquaculture Research. DOI: 10.1111/are.12790:1-5.

Interpretive Summary: Systemic granuloma is a chronic disease of uncertain etiology that has been described in several cultured fish species; this pathology is characterized by widespread granulomatous inflammation in numerous internal organs, with the absence of any associated disease agent. We described, for the first time, systemic granuloma in Atlantic salmon; this condition was observed as fish were raised to market size in a freshwater recirculation aquaculture system. Culture and 16S sequencing did not reveal the presence of an associated microorganism; special staining revealed a mineral core at the center of granulomas examined through histopathology. Although the presence of a disease agent cannot be ruled out entirely, it is likely that this condition was the result of widespread metastatic calcification of internal organs as a result of metabolic dysfunction; however, the exact pathological mechanism(s) remain unknown. Given the chronic wasting observed in highly affected fish, this condition could be very important to Atlantic salmon farmers using recirculation aquaculture systems, and therefore further research is required to further characterize, and understand the etiology of, systemic granuloma in Atlantic salmon under these culture conditions.

Technical Abstract: 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.