Addressing viral and bacterial threats to salmon farming in Chile: historical contexts and perspectives for management and control

Abstract

The rapid growth of the salmon farming industry in Chile has led to the appearance of various viral, bacterial, parasitic, and fungal pathogens affecting farmed fish. The Chilean salmon industry has suffered several health crises associated with high fish mortalities, such as caused by the infectious salmon anaemia virus (2007) and harmful algal blooms (2016). In addition to these events, marine farms are continuously affected by outbreaks of harmful pathogens, including the bacteria Piscirickettsia salmonis and, most recently, a reappearance of Renibacterium salmoninarum, and the infectious pancreatic necrosis virus. These outbreaks have led to stricter regulations, but the salmon farming industry continues to struggle despite reforms. In addition to the aforementioned pathogens, which are a continuous threat, other apparently under control pathogens have also reappeared in recent years. In this review, we analyse the current state of knowledge on four of the main pathogens affecting salmon farming in Chile. The infectious pancreatic necrosis virus is relevant as it affects freshwater‐stage fish, with survivors then acting as carriers. The infectious salmon anaemia virus currently appears to be under control; however, P. salmonis and R. salmoninarum continue to be the cause for high mortalities in the Chilean aquaculture industry.

Improved understanding of biofilm development by Piscirickettsia salmonis reveals potential risks for the persistence and dissemination of piscirickettsiosis

“…A free pass to bacterial adhesion-dependent processes, such as colonization and biofilm formation 17,42 , could take place on fish skin if P. salmonis can override the mucosal barrier. Remarkably, the interaction between fish skin mucus and P. salmonis is far from being understood, and much less is known about the persistence and infection strategies of this bacterium 49,78 . In the present study, isolate Psal-103 was sensitive to salmon skin mucus during the early stages of biofilm formation in seawater, but mucus tolerance was observed in Psal-103 biofilms from 96 h onwards (Fig.…”

Biofilm Produced In Vitro by Piscirickettsia salmonis Generates Differential Cytotoxicity Levels and Expression Patterns of Immune Genes in the Atlantic Salmon Cell Line SHK-1

“…Our results showed a delay in cell cytotoxicity caused by the bacteria, both in its planktonic and sessile form, beginning instead at 10 days p.i. Considering the P. salmonis cellular pathogenesis, these differences may be due to multiple factors that are intrinsic to the bacterium, related to its metabolic state, expression of virulence factors, its ability for survival and intracellular multiplication [ 1 , 59 ], and all this in turn may be conditioned by their planktonic and/or sessile state. In the case of Legionella pneumophila , its sessile state replicates in bone marrow-derived macrophage cells (BMDMs) with a greater capacity compared to its planktonic counterpart, also inducing lesser cell death in infected macrophages, similar to that observed for the EM-90 isolate used in this study.…”

“…Unfortunately, increased fish farming has been accompanied by the development of novel infectious-contagious diseases caused mainly by viral, parasitic, and bacterial pathogens. Piscirickettsiosis is the most prevalent bacterial disease for salmonids in Chilean aquaculture [ 1 ]. This disease is caused by Piscirickettsia salmonis , a γ-proteobacteria classified into two different genogroups associated with the LF-89 T (ATCC VR-1361) type strain and the Chilean isolate EM-90 [ 2 , 3 ].…”

Environmental issues in Chilean salmon farming: a review

“…; Figueroa et al . ). In fact, in the fattening phase in seawater, 94.7% of the antibiotics used were for piscirickettsiosis, 4.5% for Bacterial Kidney Disease (BKD) and 0.73% for other diseases (SERNAPESCA ).…”