First bioactive characterization of the skin mucus from Portugal coastal fish halobatrachus didactylus

The marine environment has several promising features for the discovery of new molecules. The oceans have half of the planet’s biodiversity and are a harsh environment for aquatic organisms challenging them to have a set of bioactive molecules to survive [1]. It is well known the mucus secreted by fish epidermis works as a defense barrier against harmful elements from the external environment [2]. Therefore, this study aimed to explore some bioactive properties such as antimicrobial activity (agar drop diffusion method), antioxidant activity (ABTS and ORAC scavenging assays) and ACE inhibitory activity (iACE) exerted by the mucus collected scraping the Halobatrachus didactylus skin, from the Tagus estuary. Direct drop application did not show inhibitory activity on the growth of E. coli and S. aureus. The protein content
in the mucus, determined by the bicinchoninic acid methodology, was 13260 ± 342 μg BSA/mL. The antioxidant activity resulted in 1.49 ± 0.04 μmol TE/mL for ABTS and 5.47 ± 0.8 μmol TE/mL for ORAC. iACE resulted in an IC50 of 60 ± 7 μg protein/mL. Also, a peptidic profile of the mucus was obtained through size exclusion chromatography showing a shortchain peptide profile (> 3000 Da) as general distribution, which is consistent with the observed bioactivities. In conclusion, fish mucus peptide fraction showed potential as an antioxidant and even more so as an antihypertensive, but not as an antimicrobial. Furthermore, more studies are needed to discover the key molecules behind these bioactivities.