Aquaculture

Genetic variation for growth in Atlantic salmon (Salmo salar) under coinfection

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Abstract

Coinfections are common during the marine phase of Atlantic salmon production and can significantly impact host performance and health. An initial infection can modulate the host immune response-either through suppression or priming-affecting susceptibility to subsequent pathogens. Understanding genetic variation in performance under such conditions is essential for developing robust selective breeding strategies. This study quantified genetic variation for growth and related robustness traits in Atlantic salmon exposed to a multi-pathogen challenge involving salmon lice (Lepeophtheirus salmonis), Salmonid alphavirus 3 (SAV3), and Piscine myocarditis virus (PMCV). A total of 1,585 PIT-tagged smolts from 98 full-sib families of the Mowi Genetics population were challenged under controlled conditions. Fish were first infested with salmon lice copepodites, lice counts were recorded at the chalimus stages (on days 8-10 post lice infection), and fish were subsequently injected with SAV3 and PMCV. Body weight was recorded at the start and end of the trial, and survival was monitored over 82 days. Three traits were analyzed: survival, growth as absolute body-weight change, and log-transformed lice count (logLC). Genetic parameters were estimated using a multi-trait Bayesian animal model with genomic relationships matrix. Mortality increased shortly after viral infection and handling but plateaued by day 40, resulting in an overall survival rate of 87%. Considerable phenotypic variation was observed for growth, with a mean body-weight gain of 63.89 g and a standard deviation of 47.03 g. Genomic heritability estimates were moderate for growth (0.23 ± 0.04) and logLC (0.20 ± 0.04), whereas survival showed low heritability on the liability scale (0.05 ± 0.03). Genetic correlations indicated no meaningful association between growth and logLC (−0.02 ± 0.16), while the correlation between growth and survival was non-significant (−0.20 ± 0.30). A strong positive genetic correlation was observed between logLC and survival (0.68 ± 0.23), although survival-related estimates should be interpreted cautiously due to low mortality and low effective sample sizes. These results show that growth under multi-pathogen coinfection is heritable and highly variable, suggesting potential for genetic improvement. The apparent genetic association between lice burden and survival also indicates that host responses to sea lice may reflect broader robustness under acute challenge conditions. Incorporating multi-pathogen challenge information into breeding programs may therefore improve the selection of Atlantic salmon with better performance and resilience in commercial grow-out environments.

Keywords: 2026

How to Cite:

Dagnachew, B., Lillehammer, M., Boison, S., Baranski, M., Werner, B., Evensen, Ø. & Gjerde, B., (2026) “Genetic variation for growth in Atlantic salmon (Salmo salar) under coinfection”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2285467. doi: https://doi.org/10.31274/wcgalp.23716

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