Correlation between three freshwater fish skin mucus antiproliferative effect and its elemental composition role in bacterial growth

Fish skin mucus acts as an immunological barrier that prevents entry of pathogens. However, there are gaps in the knowledge of microbes inhabiting skin mucus constituents to invade the host and induce pathogenecity. Hence, in the present study, skin and skin mucus of three freshwater fishes Cyprinus carpio, Labeo rohita, Cirrhinus mrigala was analyzed to compare histology and mucus activity against cancer cells. The skin mucus elemental composition and its influence on bacterial growth were also investigated. Histological examination of fish skin showed the presence of mucus secreting cells and differences in the distribution of cells were clearly seen depending on fish species. The cytotoxic potential of lyophilized skin mucus against human lung adenocarcinoma cells revealed a higher percentage of cell death at 1000 µg mL^-1 in C. mrigala skin mucus when comparing other two fish species. Elemental analysis of lyophilized skin mucus through Field Emission Scanning Electron Microscope coupled with Energy Dispersive X-ray (FESEM-EDX) confirmed the presence of carbon, nitrogen, oxygen and sulfur in C. carpio and C. mrigala. In the case of L. rohita, the element sulfur was absent. The results of bacterial growth in autoclaved skin mucus demonstrated an initial reduction in bacterial population and gradually increased over time. Initial reduction in bacteria might be due to the presence of inhibitory molecules in fish skin mucus. Subsequently, the bacteria utilize the elemental composition of skin mucus as a nutrient source to increase their growth. Study findings suggest that the presence of bioactive compounds in lyophilized skin mucus hinder the proliferation of cancer cells. Nevertheless, after autoclaving the skin mucus components, it supports the growth of bacteria due to the absence of immune molecules. The present study represents the knowledge of skin mucus composition, which could be explored further to understand how pathogens overcome the skin mucus barrier.