INTRODUCTION
Skin wound healing in Atlantic salmon (Salmo salar) is a multistep biological process encompassing re-epithelialisation, inflammation, granulation tissue formation and tissue remodelling. Impairment of any of these phases' compromises barrier restoration and fish welfare, with significant consequences for performance and resilience against pathogens like the ectoparasite sea lice. Comparative studies between salmonid species provide compelling insights into the biology of resistance. Coho salmon display near-complete resistance to sea lice, associated with a rapid epithelial hyperplasia response driven by accelerated keratocyte migration during re-epithelialisation (Salisbury et���al., 2024). Furthermore, coho salmon mount a rapid, well-localised, neutrophil-dominated inflammatory response within 24–48 hours of louse attachment, whereas Atlantic salmon exhibit a delayed and poorly localised reaction that facilitates parasite establishment (Sveen et���al., 2025). These observations collectively suggest that both the kinetics of re-epithelialisation and the quality of early inflammatory priming are critical determinants of effective skin defence. We hypothesise that targeted dietary interventions can recapitulate, in Atlantic salmon, key aspects of the wound���healing phenotype observed in resistant salmonid species. To test this, we employ an Atlantic salmon skin explant model, as New Approach Methodologies (NAMs), enabling mechanistic, tissue���level interrogation of nutritionally driven repair processes while reducing reliance on in vivo experimentation. Two complementary explant���based trials specifically address the identified rate���limiting steps in skin defence: (i) acceleration of keratocyte migration during re���epithelialisation (Trial 1), and (ii) induction of a rapid, acute inflammatory response at the wound site (Trial 2).
METHODS
Skin sections from Atlantic salmon were collected in the area between the dorsal fin and the lateral line and used as a standardised liquid���submerged skin explant culture system using an inert, non���porous support to maximise tissue viability and functional performance. Skin dissection procedures, ex-vivo wound infliction and culture conditions had a specific emphasis on preserving the skin secretome (i.e. the full set of proteins and metabolites released by the explant). Bacterial growth in culture media was monitored by optical density at 600 nm and maintained below 15% relative to baseline through scheduled medium changes. Explant viability (72 hours) was assessed via metabolic activity (Alamar Blue - resazurin assay) and membrane integrity (total protein release). Tissue stress and goblet cell activity were evaluated by quantifying total secreted mucus in the culture medium using Alcian Blue or Periodic Acid–Schiff staining coupled to colorimetric analysis. Healthy explants were defined by sustained metabolic activity and limited protein leakage throughout the assay duration. Following SOP establishment for maximal basal viability, the skin explant functional performance was used to gain new insights on the role of bioactive compounds with demonstrated or hypothesised capacity to enhance keratocyte migration (Trial 1) and compounds signalling a pathogenic insult (PAMPs), and a positive immunological control. Endpoints across both trials included gene expression profiling using panels targeting skin re-epithelialisation and inflammatory pathways.
RESULTS
Differential effects of the tested compound categories on the transcriptional upregulation of genes associated with keratocyte motility, cytoskeletal remodelling and epithelial proliferation generated new insights, on the mechanisms to accelerate the re-epithelialisation process in a wounded skin. Moreover, PAMP-based dietary treatments and insult signalling compounds primed a faster and localised neutrophilic response at the wound site, reflected in earlier upregulation of acute-phase inflammatory genes. Together, these new generated data provide integrated evidence in Atlantic salmon that several compounds (with the potential to be afterwards delivered via feed) have the potential to accelerate the re-epithelialisation phase and amplify early inflammatory priming following standardised skin wounding.
CONCLUSION
This work establishes Atlantic salmon skin explants as a practical NAM���based platform to investigate nutritionally driven modulation of skin wound healing. The data indicate that selected bioactive compounds can accelerate re���epithelialisation and enhance early inflammatory priming following skin injury, two processes that are critical for effective barrier restoration and characteristic of resistant salmonid species. These findings support the use of explant models as a screening and mechanistic tool to prioritise functional ingredients for subsequent feed formulation and in vivo validation. Ultimately, this approach may accelerate the development of nutritional strategies aimed at improving skin integrity, welfare, and resilience to ectoparasites in commercial salmon aquaculture.
Acknowledgment
This work is part of the SKINS project, Operation No. 21638 (COMPETE2030-FEDER-02247200, ALGARVE-FEDER-02247200), co financed by the European Union through the Algarve 2030 and COMPETE 2030 Operational Programs, in the framework of Portugal 2030.
References
Salisbury et al. (2024) 22:160. https://doi.org/10.1186/s12915-024-01952-8
Sveen et al. (2025). https://doi.org/10.1007/s00441-025-03976-0