In the marine environment, fish encounter various pathogenic microorganisms, prompting the development of diverse defense mechanisms. One such defense system is the epidermal mucus, which contains an array of functional compounds. Notably, this mucus comprises proteins that regulate immune responses and possess antimicrobial properties. Therefore, characterizing the composition of mucous secretions can shed light on the defense mechanisms employed by fish to safeguard themselves against infections. This becomes particularly crucial in the case of aquaculture species like Chilean croaker (Cilus gilberti), yellowtail (Seriola lalandi), and palm ruff (Seriolella violacea), which belong to different fish families, has been promoted in northern Chile. However, the defense capacity of these species against pathogens only has been analyzed in yellowtail of international waters. Hence, this study aimed to characterize the composition and antibacterial activity of protein fractions in the epidermal mucus of juvenile specimens from the aforementioned species. Initially, a comprehensive proteomic analysis employing mass spectrometry and the MASCOT tool for bioinformatics analysis was conducted to identify the proteins present in the mucus and compare their distribution based on biological function. Among all species, proteins associated with the cytoskeleton, such as actin, myosin, and keratin, were found to be the most abundant. In terms of immune composition, histone peptides emerged as the predominant molecules in all three-study species, followed by peroxiredoxin and annexin isoforms. Moreover, the antibacterial capacity of protein extracts from each species against Vibrio anguillarum and Vibrio ordalli was evaluated using turbidimetry tests and colony counts. The findings indicate that the extracts from all three species exhibited higher bactericidal activity against V. anguillarum compared to V. ordalii. This study represents an initial step toward identifying biomarkers for different physiological processes in marine fish of aquaculture interest in the northern region.

Acknowledgment: FONDECYT N°1210056