Metabolite Profiling of Epidermal Mucus of Freshwater Fish Species by HR-LCMS Analysis

Abstract

Fish epidermal mucus is the first line of defense against environmental stressors and pathogens, which plays an important role in innate immune defense, osmoregulation and chemical communication in aquatic organisms. It contains a wide range of bioactive molecules that help in maintaining the mucosal homeostasis and mediate protection against pathogens. Despite its physiological significance, the small-molecule metabolite composition has yet to be fully investigated. The present study aimed to identify metabolites present in the epidermal mucus of four economically important freshwater fish species L. rohita, H. fossilis, C. striata and O. niloticus using High Resolution Liquid Chromatography–Mass Spectrometry (HR-LCMS) in both positive and negative electrospray ionization modes. A total of 281 metabolites, belonging to diverse chemical classes including amino acids, short peptides, fatty acids and their derivatives, alkaloids, terpenoids, phenolics, were tentatively identified. Of these, 198 were found in positive ESI mode and 83 in negative ESI mode. Among these, 43 metabolites were shared by all four species, suggesting a potentially conserved mucosal metabolite profile. In fact, a few identified metabolites have been reported to have antibacterial, antifungal, antiviral, antioxidant, anti-inflammatory and anticancer properties. Some metabolite differences were also found between species, probably due to their ecological niches, feeding habits and physiology. The results demonstrate the great chemical diversity of fish epidermal mucus and its possible use as a source for bioactive compounds. This study provides insights into fish mucosal biology and supports the exploration of fish mucus metabolites for aquaculture applications, fish health monitoring, and future pharmaceutical development.