Histological structure of the skin in five fish species of Periophthalmus waltoni (Gobiidae) Silurus triostegus (Siluridae), Heteropneustes fossilis (Heteropneustidae), Mastacembelus mastacembelus (Mastacembelidae) and Coptodon zilli (Cichlidae)

The five fish species viz. Periophthalmus waltoni, Silurus triostegus, Heteropneustes fossilis, Mastacembelus mastacembelus, and Coptodon zilli were collected in the Shatt Al-Arab River from February to June 2019. The samples were transferred to the laboratory to measure their total lengths and weights. To examine the skin histology and structure in these fishes, a skin sample was taken from the dorsal part close to the lateral line. The results showed that the skin of fish contains two layers: the first is the epidermis, which includes the epithelium. The thickness of the tissue in fish varied from 3 to 20 layers. In this layer, there are mucous cells that were spared and varied in their abundance from one species to another. The dermis includes two layers of stratum spongiosum and stratum compactum. These two layers consist of pigment cells that spread directly under the epidermis in a dark brown color. In C. zilli and H. fossilis, a third layer was found under stratum compactum as hypodermis; the highest thickness of the dermis was recorded in C. zilli.