Currently, one of the primary challenges in salmon farming is caligidosis, caused by the copepod ectoparasites Caligus spp. The infection process is determined by the copepod’s ability to adhere to the fish skin through the insertion of its chitin-composed filament. In this study, we examined several antimicrobial peptides previously identified in salmonid mucosal secretions, with a primary focus on their potential to bind to chitin as an initial step. The binding capacity to chitin was tested, with hepcidin and piscidin showing positive results. Further assessments involving cytotoxicity in salmonid cells RTgill-W1, SHK-1, RTS-11, and RT-gut indicated that the peptides did not adversely affect cell viability. However, hemolysis assays unveiled the hemolytic capacity of piscidin at lower concentrations, leading to the selection of hepcidin for antiparasitic assays. The results demonstrated that the nauplius II stage of C. rogercresseyi exhibited higher susceptibility to hepcidin treatments, achieving a 50% reduction in parasitic involvement at 50 µM. Utilizing fluorescence and scanning electron microscopy, we observed the localization of hepcidin on the surface of the parasite, inducing significant spherical protuberances along the exoskeleton of C. rogercresseyi. These findings suggest that cysteine-rich AMPs derived from fish mucosa possess the capability to alter the development of the chitin exoskeleton in copepod ectoparasites, making them therapeutic targets to combat recurrent parasitic diseases in salmon farming.

The skin of fish is a physicochemical barrier that is characterized by being formed by cells that secrete molecules responsible for the first defense against pathogenic organisms. In this study, the biological activity of peptides from mucus of Seriola lalandi and Seriolella violacea were identified and characterized. To this purpose, peptide extraction was carried out from epidermal mucus samples of juveniles of both species, using chromatographic strategies for purification. Then, the peptide extracts were characterized to obtain the amino acid sequence by mass spectrometry. Using bioinformatics tools for predicting antimicrobial and antioxidant activity, 12 peptides were selected that were chemically produced by simultaneous synthesis using the Fmoc-Tbu strategy. The results revealed that the synthetic peptides presented a random coil or extended secondary structure. The analysis of antimicrobial activity allowed it to be discriminated that four peptides, named by their synthesis code 5065, 5069, 5070, and 5076, had the ability to inhibit the growth of Vibrio anguillarum and affected the copepodite stage of C. rogercresseyi. On the other hand, peptides 5066, 5067, 5070, and 5077 had the highest antioxidant capacity. Finally, peptides 5067, 5069, 5070, and 5076 were the most effective for inducing respiratory burst in fish leukocytes. The analysis of association between composition and biological function revealed that the antimicrobial activity depended on the presence of basic and aromatic amino acids, while the presence of cysteine residues increased the antioxidant activity of the peptides. Additionally, it was observed that those peptides that presented the highest antimicrobial capacity were those that also stimulated respiratory burst in leukocytes. This is the first work that demonstrates the presence of functional peptides in the epidermal mucus of Chilean marine fish, which provide different biological properties when the fish face opportunistic pathogens.

In the search for safe and effective natural antioxidants, this study investigates the antioxidant and cytotoxic properties of aqueous extracts obtained from three fungi of the family Hymenochaetaceae: Inonotus sp., Fulvifomes sp., and Phylloporia boldo, all associated with endemic trees of the Chilean sclerophyll forest. Antioxidant capacity was assessed through DPPH, ABTS, and hydroxyl radical scavenging assays. Fulvifomes sp. exhibited the highest antioxidant activity across all methods, which was consistent with its elevated polyphenol content. P. boldo, on the other hand, had the highest protein concentration but comparatively lower antioxidant activity. Cytotoxicity was evaluated using the WST-1 assay in the RTgill-W1 salmonid cell line, revealing that Inonotus sp. displayed the lowest cytotoxicity at both tested concentrations, suggesting it may be suitable for bioactive applications in aquaculture. In contrast, Fulvifomes sp. and P. boldo showed significant cytotoxic effects at higher concentrations. These findings highlight the potential of Inonotus sp. as a natural antioxidant with low cytotoxicity and encourages further exploration of native forest fungi as sources of functional bioactive compounds for food, nutraceutical, or aquaculture applications.

The objective of this study was to identify and experimentally validate novel antioxidant peptides derived from salmon collagen through an integrated bioinformatic and experimental workflow. Collagen sequences from Salmo salar were subjected to in silico enzymatic hydrolysis, and the resulting peptides were characterized using physicochemical descriptors. Principal component analysis and k-means clustering were then applied as exploratory tools to prioritize candidates displaying physicochemical proximity to previously reported antioxidant peptides. The selected candidates were chemically synthesized, purified, and evaluated at concentrations of 0.2 and 0.4 mM using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging assay, the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical-scavenging assay, and a cellular antioxidant activity assay, with vitamin C as a positive control. Cytotoxicity was assessed using the WST-1 assay. The peptide AS-5390 (DGCERCF) demonstrated superior radical scavenging capacity, with activity comparable to that of vitamin C in the DPPH assay at 0.2 mM and maintaining antioxidant activity in the ABTS assay at both tested concentrations. The peptide AS-5394 (PGDIG) exhibited the strongest cellular antioxidant response, reaching approximately 40% activity at 0.4 mM. Both peptides maintained high cell viability. Overall, this integrated strategy enabled the identification of salmon collagen-derived peptides with assay-dependent antioxidant activity and potential applications as functional food or nutraceutical ingredients.