Abstract

Fish epidermal mucus acts as a primary barrier against pathogens and environmental stressors, while also playing a key role in physiological processes such as osmoregulation and sensory perception. This study examines the proteomic composition and antimicrobial properties of epidermal mucus from juveniles of the marine species Seriola lalandi, Seriolella violacea, and Cilus gilberti, which are being considered for diversification of Chilean aquaculture. The results showed that, although S. violacea juveniles secreted five times more mucus than C. gilberti and S. lalandi, the total protein content per mL did not differ significantly for S. lalandi and was twice the amount found in C. gilberti mucus. Proteomic analysis across all mucus samples from the studied fish species identified a diverse array of proteins involved in cellular structure, metabolism, immune responses, oxidative stress management, and proteolysis. Protein-protein interaction networks indicated that translation is the dominant process in the skin mucus of the three fish species, underscoring the necessity of continuous protein synthesis for maintaining skin integrity and barrier function. The activation of energy-generating pathways further suggests a coordinated metabolic response to sustain ATP supply for ongoing protein production. Antimicrobial assays demonstrated that the mucus exhibits activity against Vibrio strains-common aquaculture pathogens-underscoring its protective role. Enzymatic analyses confirmed the lysozyme and peroxidase activity, key components of the innate immune defense in these mucosal barrier. Overall, these results demonstrate that epidermal mucus is a multifunctional fluid integrating immune defense, environmental adaptation, and physiological homeostasis. Additionally, the protein profile of mucus can serve as a non-invasive biomarker for health status, providing insights into pathogen exposure, nutritional condition, and stress responses in these aquaculture-relevant fish species.