Fish skin is, in fact, its first body defense line. The general skin structure is roughly similar in all fishes. It consists of two main layers: epiderm that covers the outer surface of a fish body, and its sub-layer called hypoderm that forms the inner layer. In this research, a number of 25 healthy mature Epinephelus coioides fish, with the same size and weight, from both genera were studied. For microscopic studies, cuttings from different skin areas of the fish including its head, upper lip, lower lip, dorsal and ventral trunk and tail fin, 6 μm in thickness each, were provided and stained through PAS and H & E methods. The distribution of mucus cells was studied on a scale of 100 μm2 in epiderm. It was observed that mucus cells mainly lie in the middle to outer layers of epiderm and their distributions differ in various skin areas of the fish. Moreover, cytoplasm in mucus cells shows a positive reaction to PAS staining; therefore, they are differentiated from other epiderm cells in this way. Histometric studies illustrated that distributions of mucus cells in varying parts have significant difference (p≤ 0.05). However, they were not significantly different in the areas such as upper lip, lower lip dorsal and ventral trunk. According to the distribution pattern of mucus cells, the skin in Epinephelus coioides may be classified into four areas such as head, upper lip and lower lip, dorsal trunk as well as ventral trunk and tail stem.
