Exploring genetic resistance to infectious salmon anemia virus in captive north american salmon (salmo salar)

Authors: JOHNSTON, AMBER - University Of Maine; BOUCHARD, DEBORAH - University Of Maine; TURNER, SARAH - University Of Maine; Lifgren, Demitri; Polinski, Mark

Submitted to: Western Fish Disease Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 7/29/2024
Publication Date: 7/30/2024
Citation: Johnston, A.E., Bouchard, D.A., Turner, S.M., Lifgren, D.L., Polinski, M.P. 2024. Exploring genetic resistance to infectious salmon anemia virus in captive north american salmon (salmo salar) (abstract). Western Fish Disease Workshop. 07302024.

Interpretive Summary:

Technical Abstract: For over 20 years, the National Cold Water Marine Aquaculture Center (NCWMAC) has selectively bred Atlantic salmon for improved aquaculture performance including increased growth and sea lice resistance. In this study, we sought to determine if these selective breeding approaches have incidentally affected fish susceptibility to infectious salmon anemia virus (ISAV) and/or resistance to its associated commercially impactful disease – infectious salmon anemia (ISA). We further sought to investigate if variations in family-based resistance to ISAV and/or ISA could be used to identify mechanisms for generating a resistant salmon phenotype. To do this, 40 families (30 selectively bred for aquaculture production and 10 reference control families) were first divided into 16 replicate tanks for family survival analyses with one salmon per family per tank. Four fish per family were exposed to ISAV via intraperitoneal injection (104 TCID50ml-1) while the remaining fish per family were exposed by cohabitation. Additionally, four tanks each containing one fish per family were exposed via cohabitation with ISAV injected mixed-family-origin fish and utilized for periodic tissue sampling. Survival analyses revealed no significant difference in outcome between injected or cohabitated fish; yet cumulative mortality across the 40 families ranged from 25 to 94%, with significant differences observed between the most and least susceptible families. Survival analyses also revealed no difference in mean survival between selectively bred and control families, suggesting that current NCWMAC selective breeding approaches have not incidentally impacted ISAV resistance. Further, RT-qPCR screening identified viral loads in the spleen to be consistently as high or higher relative to gill, heart, or kidney of infected fish, and that these loads were not lower in fish of resistant families compared to susceptible families. This data, in concert with the observation that disease timing (although not outcome) was similar between resistant and susceptible families, suggests that phenotypic resistance may be decided later in the infection process and involves mechanisms that enhance host damage control processes rather than suppressing viral replication. Future research will focus on transcriptome mapping of fish from resistant versus susceptible families for better determining the pathways involved in establishing an ISAV resistant phenotype.