Biochemical Components, Immune Characteristics and Antimicrobial Activity of Epidermal Mucus of the Three Indian Major Carp Species

Abstract

Fish live in an environment that is full of phylogenetically diverse collections of bacterial pathogens. Fish epidermal mucus is regarded as a barrier between fish and infectious microorganisms in their surroundings protecting it against pathogens. The current study aimed to evaluate the biochemical components of skin mucus, mucosal immunity, and the bactericidal effect of epidermal mucus in three carp species, including Catla catla, Labeo rohita, and Cirrhinus mrigala. Biochemical composition showed the presence of protein, carbohydrate and lipid in the mucus of all three carp species, and concentration varied with respect to species. Protein and lipid were higher in C. catla, followed by L. rohita and C. mrigala; whereas, carbohydrate was high in the mucus of C. mrigala. Mucosal immunity indicating parameters, viz. lysozyme, alkaline phosphatase, myeloperoxidase, and protease activity was observed in the epidermal mucus of these species, showing the role of mucus in immunity. Lysozyme and alkaline phosphatase were high in C. mrigala, and myeloperoxidase and protease were high in C. catla. To understand the bactericidal role of raw and aqueous mucus, extracts of the epidermis of these species were tested against the common fish pathogen Aeromonas hydrophila by a well diffusion assay. The results showed that raw as well as aqueous extracts showed the zone of inhibition (ZOI) against A. hydrophila; however, ZOI was high for raw mucus compared to aqueous extract. The variation in biochemical composition and mucosal immunity parameters may be due to variation in their habitat, ecological niche, and the presence of pathogens in the surrounding medium.