Biological and Ecological Roles of External Fish Mucus: A Review

Abstract

Fish mucus layers are the main surface of exchange between fish and the environment, and they possess important biological and ecological functions. Fish mucus research is increasing rapidly, along with the development of high-throughput techniques, which allow the simultaneous study of numerous genes and molecules, enabling a deeper understanding of the fish mucus composition and its functions. Fish mucus plays a major role against fish infections, and research has mostly focused on the study of fish mucus bioactive molecules (e.g., antimicrobial peptides and immune-related molecules) and associated microbiota due to their potential in aquaculture and human medicine. However, external fish mucus surfaces also play important roles in social relationships between conspecifics (fish shoaling, spawning synchronisation, suitable habitat finding, or alarm signals) and in interspecific interactions such as prey-predator relationships, parasite–host interactions, and symbiosis. This article reviews the biological and ecological roles of external (gills and skin) fish mucus, discussing its importance in fish protection against pathogens and in intra and interspecific interactions. We also discuss the advances that “omics” sciences are bringing into the fish mucus research and their importance in studying the fish mucus composition and functions.

Evaluation of the antibacterial activity of skin mucus of three carp species

“…It is now well established that fish skin mucus acts as mechanical barrier to fishes by lying at interface between them and surrounding pathogens (Reverter et al 2018). In addition to trapping and sloughing of infectious pathogens, the skin mucus is the reservoir of antimicrobial components which acts in different ways and is gifted with innate antibacterial ability as reported by Nagashima et al (2001).…”

“…Further, many authors (Alvarez-Pellitero 2008; Guardiola et al 2014;Hedmon 2018) have demonstrated that mucus also acts as a storehouse for innate immune components such as lectins, pentraxines, lysozymes, proteolytic enzymes, alkaline phosphatase, C-reactive protein, complement, and antimicrobial peptides (AMPs) as well as immunoglobulins which provide antibacterial strength to fish skin mucus. In recent years, many investigators have investigated the antibacterial properties of skin mucus from many a fish species against several human and fish pathogenic microbes (Wei et al 2010;Bragadeeswaran and Thangaraj 2011;Vennila et al 2011;Fuochi et al 2017;Reverter et al 2018) which supported the hypothesis that the epidermal mucus plays a protective role and should be effective against fish and human pathogenic bacteria as well. However, comprehensive information on the antimicrobial activity of epidermal mucus in fresh water fishes of different habits and habitats is still lacking.…”

Physicochemical Properties of African Catfish Mucus and Its Effect on the Stability of Soya Milk Emulsions

“…The images at 50 and 100 nm were taken to quantify the particle size of each soya milk globule and its distribution in each emulsion sample using the method described by [60]. The particle size distribution of ACM-stabilized emulsions was elucidated by calculating Sauter mean diameter (D (3,2) ) using Equation (1) while the standard deviation i.e., value of the width of the milk goblets distribution in the ACM-stabilized emulsion was calculated using Equation (2). The average droplet size is given by Equation (3) where n i is the number of goblets in each size class, d i is the particle diameter, ni is the total number of droplets, and d n is average droplet size [61].…”

“…Fish skin mucus, a waste product, is a substance produced when the fish undergoes stress. Mucus obtained from fish has anti-microbial and lubricating properties; and contains proteins, sugars and nucleic acid [1][2][3]. The disposal of this mucus has raised economic and environmental concerns for the fish industry in recent times [4,5].…”

Exploring sample cross‐contamination in fish epidermal mucus

“…In addition, because it is continuously secreted and replaced, the composition of a fish's epidermal mucus can provide information on the fish's physiological condition (Subramanian et al ., ). Unfortunately, due to its adhesive character resulting from low‐affinity bonds made by mucins [flexible arrays of proteins covalently bonded to carbohydrate chains (Cone, )] epidermal mucous samples are extremely susceptible to cross‐contamination through contact between individuals, contaminated surfaces and other tissues (Reverter et al ., ).…”