Infectious salmon anemia virus susceptibility and health status of wild versus farmed Atlantic salmon: A comparative study
There are concerns about the potential interaction between farmed and wild Atlantic salmon in areas where they coexist. The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) has designated wild Atlantic salmon populations in Atlantic Canada as threatened or endangered. While the health status and disease resistance of farmed Atlantic salmon is well documented, the information for wild Atlantic salmon is less abundant. For example, Infectious Salmon Anemia Virus (ISAV) remains a recurrent problem for cultured salmon in Atlantic Canada, with outbreaks detected in Nova Scotia and Newfoundland since 2012. There are knowledge gaps regarding the prevalence of this virus in wild populations as well as the potential transmission between wild and cultured stocks. As such, the aim of this project was to use in vivo disease challenges and next generation sequencing technologies to compare the susceptibility of wild Atlantic salmon stocks (St. John River, Inner Bay of Fundy, Miramichi, Margaree river stocks) and cultured stocks (St. John River origin) to diseases such as ISAV and others. This study examined genetic differences and measure immune responses, which could potentially explain any observed differences in susceptibility of wild and cultured salmon to ISAV. It also provided a general assessment of the health status of wild stocks. The evolution rate of ISAV was examined by looking at full ISAV sequences in tissue of farmed and wild Atlantic salmon sampled throughout the course of the in vivo challenges. This project addressed the knowledge gap regarding the susceptibility of wild Atlantic salmon compared to farmed Atlantic salmon to ISAV.
The progress of ISAV infection in blood from cohabitant fish was monitored through time. ISAV strains tested were a high virulent (i.e., ISAV HPR4) and a mid-virulent (i.e., NS 2012-21) isolate. For the high virulent ISAV, all wild salmon stocks had better survival than the farmed stock. Farmed fish had a 2 % survival. However, the St-John River stock survival was poor with around 10 % survival. The ISAV viral loads of the Miramichi and Big Salmon River were lower and these groups of fish also experienced less mortality. With the mid-virulent ISAV isolate, survival was better, with 87 % for farmed fish and 95 % for the wild salmon stocks on average. Genes expressed in gills of infected fish revealed responses against ISAV that have been previously observed (Leblanc et al 2012). Comparison of gene expression amongst fish stocks revealed differences in resistance to ISAV. The true evolution rate of ISAV could not be measured with the method selected, i.e. the rolling circle reverse transcriptase method, mainly because viral RNA was not sufficiently abundant compared to host RNA. This method would not recommended for in vivo viral evolution studies.
2014 - 2017
Research Scientist, Gulf Fisheries Centre
343 Université Avenue, Moncton, New Brunswick
Mark Hambrook, Miramichi Salmon Association
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