On the epidermal structure of Boleophthalmus and Scartelaos mudskippers with reference to their adaptation to terrestrial life

Abstract

The skin structures of 4 species of oxudercine gobies (3 species ofBoleophthalmus and 1 species ofScartelaos) were investigated in relation to the terrestrial exposure of these fishes. These species have similarities in both lifestyle and skin structure. The specializations for terrestrial life mainly include the presence of dermal bulges, a thick middle cell layer, and a vascularized epidermis. Moreover, mucous cells are distributed only on the epidermis where the capillaries are undeveloped. In all species, the dermal bulges are large on the head and dorsal body, which are most often exposed to the air, and push up a thin epidermis, forming so-called papillae. Capillaries are densely distributed on the apical area of each papilla. InBoleophthalmus, the middle cell layer is thicker, the bulges are larger and distributed over a greater part of the body, and the area of the skin surface having the papillae is larger than it is inScartelaos. These differences suggest that the contribution of the skin to respiration is comparatively large inBoleophthalmus species, reflecting their more frequent activities on mudflats relative to the activities of theScartelaos species, which prefer to stay in the water. Mucous cells are abundantly distributed on the epidermis surface between the papillae in all species. The separation of the capillaries and the mucous cells may be due to an impeding of gas exchange by the mucus.