There is an increased interest in identifying beneficial compounds of plant origin that can be added to animal diets to improve animal performance and have a health-promoting effect. In the present study, nine herb species of the Norwegian wild flora or which can be cultivated in Norway were selected for phytogenic evaluation (hops, maral root, mint, oregano, purslane, rosemary, roseroot, sweet wormwood, yarrow). Dried herbs were sequentially extracted with dichloromethane (DCM), ethanol (EtOH) and finally water (H₂O) by ultrasound-assisted extraction (UAE). The UAE protocol was found to be more rational than conventional Soxhlet with respect to DCM extraction. Total extraction yield was found to be highest for oregano (Origanum vulgare) with 34.4 g 100⁻¹ g dry matter (DM). H₂O-extracts gave the highest yields of the three solvents, with up to 25 g 100⁻¹ g DM for purslane (Portulaca oleracea ssp. sativa) and mint (Mentha piperita). EtOH- and H₂O-extracts were the most efficient extracts with respect to free radical scavenging capacity (ABTS (=2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), and oregano, mint, hops (Humulus lupulus) and maral root-leaves (Leuzea carthamoides) were found to be the most efficient antioxidant sources. Hops (EtOH-extract) contained α- and β-acids, xanthohumols, chlorogenic acid and the hitherto unreported 3-O-glucosides of kaempferol and quercetin. Maral root-leaves contained among other compounds hexosides of the 6-hydroxy- and 6-methoxy-kaempferol and -quercetin, whereas roseroot (Rosea rhodiola) revealed contents of rosavin, rhodiosin and rhodionin. Sweet wormwood (Artemisia annua) contained chlorogenic acid and several derivatives thereof, scopoletin and poly-methylated flavones (eupatin, casticin, chrysoplenetin). Antimicrobial potential of different plant extracts was demonstrated against Gram-positive and Gram-negative bacteria using the indicator organisms Staphylococcus aureus, and Escherichia coli, and the Atlantic salmon bacterial pathogens Moritella viscosa, Tenacibaculum finnmarkense and Aliivibrio wodanis. DCM extracts possessed the highest activities. Data demonstrate the potential ability of herb extracts as natural antimicrobials. However, future safety studies should be performed to elucidate any compromising effect on fish health.

Proteins present in blood samples from Atlantic salmon (Salmo salar) infected with salmon lice (Lepeophtheirus salmonis) were analyzed using liquid chromatography–high-resolution mass spectrometry. Bioinformatic analyses revealed 1820 proteins, of which 58 were assigned to lice. Among these, peroxiredoxin-2, an antioxidant protein, was found relevant with respect to blood feeding of the parasite. The three-dimensional structure analysis of the protein revealed a surface amino acid sequence of interest. A 13-amino-acid peptide was selected as a potential antigen due to its predicted solubility, antigenicity, probable non-allergenic, and non-toxic nature. This peroxiredoxin-2-derived peptide was synthesized, combined with a commercially available adjuvant, and used for vaccination. The test vaccine demonstrated a 60–70% protection rate against early-stage Lepeophtheirus salmonis infection in a challenge trial in Norway. Additionally, the vaccine was tested against salmon lice (Caligus rogercresseyi) in Chile, where a remarkable 92% reduction in the number of adult lice was observed. Thus, in combination with the selected adjuvant, the peptide showed antigenic potential, making it a suitable candidate for future vaccine development. The approach described holds promise for the development of peptide vaccines against various ectoparasites feeding on blood or skin secretions of their hosts.

Cell lines and primary cultures are widely used to study host-pathogen interactions, reducing the need for challenge trials with live fish, which are costly and raise ethical concerns. We present Atlantic salmon scale explants (SE) as a promising model for bacterial challenges. Comparison with the body map (transcriptomes of seventeen cells and tissues) revealed strong immune activity in SE. SE ranked first in antiviral gene expression and second and third in antibacterial and inflammatory responses, respectively. Additionally, SE shows high expression of skin-specific genes encoding structural proteins of the cytoskeleton and extracellular matrix. Contrast to the epidermis, dermis, and whole skin highlights immune genes, including markers of acute inflammation and stress. Exposure to pathogens (Moritella viscosa and Tenacibaculum finnmarkense) and commensal bacteria consistently upregulated a suite of immune genes in a dose response manner. This panel includes chemokines, cytokines, genes involved in eicosanoid metabolism, and both humoral and cellular effectors. The prevalence of genes related to signaling and communication suggests that salmon scales function as sentinels, mobilizing immune responses upon encountering bacteria. While common immune responses were evident across all trials, scales also revealed differences between bacterial species. Combining commensal bacteria with M. viscosa enhanced responses to pathogens, and differences were observed between M. viscosa and T. finnmarkense. The effects of commensal bacteria varied in magnitude. Exposed cells showed changes in morphology and increased iNOS expression. Future development of this model will focus on time-course experiments and expanding the analytical repertoire to include pathology detection methods.

A new polypeptide vaccine towards salmon lice (Lepeophtheirus salmonis) was given to experimental groups of 2 × 8000 Atlantic salmon parr (Salmo salar L.), following the vaccination of a total of 4 × 8000 parr with a common set of vaccines used in Norwegian aquaculture to prevent infestation in salmon growing at sea. The remaining 2 × 8000 salmon served as control. The trial was conducted at a sea farm research facility at Knappen-Solheim in Masfjorden, Norway. Natural infestation with sea lice were staged and counted once a week from January–December 2023. The infestation was never above two mature female lice per salmon, the maximum limit set specifically for the present trial by the Norwegian Food Safety Authorities, thus delousing with chemicals or other methods was avoided. Mortality, growth, feed consumption, sexual maturation, slaughter quality, and welfare quality parameters were not significantly different between vaccinated and control salmon. The effect size showed a moderate positive difference of 0.07 mature female salmon lice per salmon in favor of the vaccinated groups from a fish size above 600 g in May until November. All fish were slaughtered and marketed at a size of 5.8 kg (>83% superior quality).

Reduced fish oil (FO) inclusion in salmon feeds has lowered dietary EPA (20:5n-3) and DHA (22:6n-3), highlighting the need to better understand how their levels and relative ratios affect fish performance, health, and fillet quality. This study used three diets in triplicate commercial-scale cages in seawater (Oct 2022 – Jan 2024) under challenging farming conditions in Arctic Finnmark, Norway. Diets contained 7.5 % or 10 % EPA+DHA of total fatty acids (FA), supplied by FO or equal parts FO and DHA-rich algal oil (AO): FO7.5 (EPA:DHA 0.6), FO10 (1.7), and FO5AO5 (0.3). Final body weight reached 4.8 kg in FO7.5 and FO5AO5 and was 0.6 kg lower in FO10 (P = 0.08). FO10 showed lowest mortality (6.5 % vs. 9 %; P = 0.008), mainly due to fewer and smaller skin wounds (r = 0.91, P < 0.0001), but also less heart-related losses (P < 0.01). Handling-related mortality was higher in FO7.5 than FO5AO5 (P = 0.03), but not FO10 (P = 0.11). Reduced wounds in FO10 increased harvest superior-grades (P < 0.004), associated with higher EPA levels (r = −0.76, P < 0.03), but not DHA. In vitro exposure of scale explants to Moritella viscosa linked FO10 to improved skin health through enhanced wound repair, immune activation, and metabolic regulation. FO10 fish had larger hearts, smaller livers, and lower slaughter yield, while FO7.5 had highest distal intestinal mucosal atrophy at harvest (P = 0.04), higher fillet fat than FO10 (P = 0.03), and higher skin fat than FO5AO5 (P = 0.02). FO10 and FO5AO5 had highest EPA+DHA fillet levels, with FO10 yielding highest EPA and FO5AO5 highest DHA. Dietary FA’s significantly regulated lipid partitioning and storage patterns among tissues. Both FO10 and FO5AO5 had reduced fillet gaping, while FO5AO5 fillets were paler and softer. Overall, EPA-rich diets improved resilience under infectious stress, enhancing wound repair, heart health, survival and product quality. These benefits occurred alongside lower slaughter yield and seemingly lower growth of FO10, highlighting trade-offs in diet evaluation where growth, health, and product quality may diverge.

A new polypeptide vaccine towards salmon lice (Lepeophtheirus salmonis) was given to experimental groups of 2 x 8000 Atlantic salmon parr (Salmo salar L.), following the vaccination of a total of 4 x 8000 parr with a common set of vaccines used in Norwegian aquaculture to prevent infection in salmon growing at sea. The remaining 2 x 8000 salmon served as control. The trial was conducted at a sea farm research facility at Knappen-Solheim in Masfjorden, Norway. Natural infection with sea lice were staged and counted once a week from January – December 2023. The infection was never above 2 mature female lice per salmon, maximum limit set specifically for the present trial by the Norwegian Food Safety Authorities, thus delousing with chemicals or other methods was avoided. Mortality, growth, sexual maturation, slaughter quality and welfare quality parameters were not significantly different between vaccinated and control salmon. The vaccine had a minor positive effect on salmon lice development. All fish were slaughtered and marketed at a size of 5.8 Kg (> 83 % Superior quality).