Prolonged exposure to cold temperatures largely delays the Atlantic salmon’s (Salmo salar) innate immune response to formalin-killed Tenacibaculum maritimum

Citation

Rojas I, Caballero-Solares A, Hall J, Sandrelli R, Clow K, Swanson AK & Gamperl AK (2025) Prolonged exposure to cold temperatures largely delays the Atlantic salmon’s (Salmo salar) innate immune response to formalin-killed Tenacibaculum maritimum. SSRN. https://doi.org/10.2139/ssrn.5854931

Abstract
Extreme cold-water events are expected to increase in frequency in the Northern Atlantic, and over the past decade there has been a re-emergence of cold temperature-associated bacterial diseases at Atlantic salmon sea-cages. Surprisingly, few studies have examined the effects of prolonged exposure to winter temperatures (≤ 2°C) on the immune function of fishes, and specifically the ability of Atlantic salmon to mount an immune response to bacterial challenges. We held post-smolt salmon at 8 and 2°C for six weeks, and then intraperitoneally injected them with a formalin-killed Tenacibaculum maritimum. We measured key components of the innate immune response [blood respiratory burst (RB) and lysozyme activity, and the expression of 21 immune-related genes (transcripts of interest, TOI) in the spleen] prior to injection (i.e., constitutive levels) and at 6-, 12-, 18-, 24-, 48- and 72-hours post-injection. RB was lower at 2°C and following T. maritimum injection, and this was more evident at 2°C. In contrast, neither of these changes were evident for lysozyme activity. Expression of 20 of the 21 TOI was affected by bacterin injection in fish held at 2 and/or 8°C. Fish at 2°C had a delayed up-regulation for seven TOI (tlr5s, ccl19b, cox2, hampa, il8a, ch25ha and socs3). However, the magnitude of the response was only different between temperatures for four TOI (the change in expression of alox5b and hampa greater, whereas that of campb and lect2 lower). These data show that winter-like temperatures negatively impact some components of the salmon's immune response, potentially increasing their susceptibility to bacterial diseases.

Keywords
salmon farming; winter; bacterial stiimulation; tenacibaculosis; immunity