Morphology of mucous glands in the skin of breeding and non-breeding aquatic frog, Euphlyctis cyanophlyctis (Dicroglossidae)

The changes in environmental conditions incur morphological alterations in animal tissues. Amphibians have adapted to diverse habitats, wherein their skin, plays a vital role in protecting them from fluctuating environmental conditions. In the present study, we investigated the morphology of skin and chemical composition of skin glands using histochemical methods in the widely distributed aquatic frog Euphlyctis cyanophlyctis. We identified two types of mucous glands (ordinary and specialized) and one type of serous gland in both the dorsal and ventral skin of the frogs collected in breeding and non-breeding seasons. Both types of mucous glands were positive for mucopolysaccharide staining, and serous glands were positive for protein staining. The density of specialized mucous glands was higher than ordinary mucous glands. The skin of non-breeding frogs was characterized by large-sized mucous glands in high numbers as compared to breeding frogs. In the ventral skin, the density of mucous glands was high and their sizes were larger when compared with the dorsal skin. The results suggest that the secretion of mucous glands is involved in preventing water loss during the non-breeding season, thereby protecting them from high temperatures in summer. The mucoid secretion is possibly facilitating frog movements in the water.