Salinity change evokes stress and immune responses in Atlantic salmon with microalgae showing limited potential for dietary mitigation

Doret R van Muilekom; Jonas Mueller; Jacqueline Lindemeyer; Thekla Schultheiß; Edmund Maser; Henrike Seibel; Alexander Rebl; Carsten Schulz; Tom Goldammer

doi:10.3389/fphys.2024.1338858

Salinity change evokes stress and immune responses in Atlantic salmon with microalgae showing limited potential for dietary mitigation

Front Physiol. 2024 Feb 12:15:1338858. doi: 10.3389/fphys.2024.1338858. eCollection 2024.

Authors

Doret R van Muilekom^#¹, Jonas Mueller^#^{2

3}, Jacqueline Lindemeyer⁴, Thekla Schultheiß⁴, Edmund Maser⁴, Henrike Seibel³, Alexander Rebl¹, Carsten Schulz^{2

3}, Tom Goldammer^{1

5}

Affiliations

¹ Fish Genetics Unit, Institute of Genome Biology, Research Institute for Farm Animal Biology (FBN), Dummerstorf, Germany.
² Department for Marine Aquaculture, Institute of Animal Breeding and Husbandry, Kiel University, Kiel, Germany.
³ Fraunhofer Research Institution for Individualized and Cell-Based Medical Engineering IMTE, Aquaculture and Aquatic Resources, Büsum, Germany.
⁴ Institute of Toxicology and Pharmacology for Natural Scientists, University Medical School Schleswig-Holstein, Kiel, Germany.
⁵ Faculty of Agriculture and Environmental Sciences, University of Rostock, Rostock, Germany.

^# Contributed equally.

Abstract

Smoltification was found to impact both immune and stress responses of farmed Atlantic salmon (Salmo salar), but little is known about how salinity change affects salmon months after completed smoltification. Here, we examined (1) the effect of salinity change from brackish water to seawater on the stress and immune responses in Atlantic salmon and (2) evaluated if functional diets enriched with microalgae can mitigate stress- and immune-related changes. Groups of Atlantic salmon were fed for 8 weeks with different microalgae-enriched diets in brackish water and were then transferred into seawater. Samples of the head kidney, gill, liver and plasma were taken before seawater transfer (SWT), 20 h after SWT, and 2 weeks after SWT for gene-expression analysis, plasma biochemistry and protein quantification. The salmon showed full osmoregulatory ability upon transfer to seawater reflected by high nkaα1b levels in the gill and tight plasma ion regulation. In the gill, one-third of 44 investigated genes were reduced at either 20 h or 2 weeks in seawater, including genes involved in cytokine signaling (il1b) and antiviral defense (isg15, rsad2, ifit5). In contrast, an acute response after 20 h in SW was apparent in the head kidney reflected by increased plasma stress indicators and induced expression of genes involved in acute-phase response (drtp1), antimicrobial defense (camp) and stress response (hspa5). However, after 2 weeks in seawater, the expression of antiviral genes (isg15, rsad2, znfx1) was reduced in the head kidney. Few genes (camp, clra, c1ql2) in the gill were downregulated by a diet with 8% inclusion of Athrospira platensis. The results of the present study indicate that salinity change months after smoltification evokes molecular stress- and immune responses in Atlantic salmon. However, microalgae-enriched functional diets seem to have only limited potential to mitigate the related changes.

Keywords: functional feed; immunity; microalgae; salinity; salmon; smoltification.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was funded by the BMBF within the project BioFiA (Project numbers 031B09151E1, 031B09151E2, 031B09151E8) and the project AQUATOR (Project number 031B0915H3).