Epidermal mucus serves as a physiological and immunological first line of defense to maintain normal physiological status in Teleost fish.  It offers protection against pathogenic infections and environmental contaminants. The ability of mucus as a protector depends on its bioactive components, such as high-molecular-weight glycoproteins, lysozyme, alkaline phosphatase, immunoglobulin, complement proteins, C-reactive proteins, lectins, agglutinin, interferon, vitellogenin, proteases, antimicrobial proteins, antimicrobials peptides, calmodulin, crinotoxins, pheromone, cytokines, acute-phase proteins, carbonic anhydrase, hemolysin, serotransferrin, heat shock proteins, superoxide dismutase, and pentraxins.  Cortisol, glucose, lactic acids, reactive oxygen species, and cellular antioxidants were also detected in the epidermal mucus and have the potential as stress biomarkers. Aside from its potential as a biological matrix to assess the immunity and health status of fish, epidermal mucus also serves as an ecotoxicological biomonitoring tool by detecting biochemical biomarkers responses that arise. We encourage future studies to assess the potentials of the epidermal mucus biological activity using the proteomics approach, given the diversity of fish species.  Knowledge about fish health and welfare is important for the conservation and preservation of species biodiversity