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Temperature-dependent physiological impairment and mortality of wild post-smolt Atlantic salmon exposed to salmon lice
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DOI：10.1093/icesjms/fsag118.png)
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Abstract
En 中文
The marine ectoparasite Lepeophtheirus salmonis (salmon louse) constitutes a significant threat to wild and farmed Salmo salar (Atlantic salmon) in intensive aquaculture regions of the North Atlantic. The effects of L. salmonis on wild salmon remain poorly understood, as field studies, the predominant research approach for wild salmon, often fail to account for individuals that die from infection. We investigated the combined effects of L. salmonis infection intensity and water temperature (13, 10, 7°C) on 321 post-smolt S. salar (17.3 ± 5.0 g; condition factor: 0.9 ± 0.1) captured in the wild and brought into tank facilities. Infection intensity was negatively associated with survival probability, whereas temperature had a comparatively smaller effect. The bootstrapped 50% mortality risk threshold was estimated at 0.54 lice g-1 (95% CI: 0.44–0.62), based on a generalized linear mixed-effects model (marginal R² = 0.875). Final weight, specific growth rate (SGR), and condition factor varied across temperatures, with fish at lower temperatures showing higher growth and better condition, possibly due to the longer duration of the trial at lower temperatures, which allowed for more feeding opportunities, as all temperature treatments were run until lice reached the adult stage. The onset of mortality aligned with the development of female preadult lice, which was strongly temperature-dependent. SGR was significantly reduced for the Mortalities compared to the Survivors across all temperatures (t-test and Wilcoxon rank-sum; p < 0.01). Condition was most severely affected at 13°C, with Mortalities showing significantly reduced values compared to Survivors (Wilcoxon; p < 0.01). Osmoregulatory impairment in moribund fish was generally high and greater at higher temperatures. Across temperatures, infection intensity had inconsistent effects on CSI, HSI, and %DWL, calling into question their reliability as fitness indicators for fish of the size used in this study. As the salmon used in this study were sourced from a single river population, population-specific immune and microbiome differences may limit the generality of these findings across wild Atlantic salmon populations. Collectively, this study highlights L. salmonis as a major driver of increased mortality, reduced growth potential, and osmoregulatory stress in wild post-smolt salmon across the studied temperature range.
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