The Influence of Mucus on the Diffusion of Water across Fish Epidermis

An assessment of the role of mucus on the water impermeability of fish epidermis has been made for the marine elasmobranch, Raja clavata. Surface mucus is interpreted as an unstirred layer. The experimental work measured variation of the diffusional coefficient of mucus for water with changing mucus concentration and estimates the in vivo concentration of mucus on the skin. Mucus does restrict the diffusion of water, but the contribution of this resistance to the impermeability of fish epidermis to water diffusion is unlikely to exceed 10% of the overall value. Other ways by which mucus might influence water movements are discussed.