University of Isfahan Taxonomy and Biosystematics 3115-9001 14 51 2022 08 23 A Histological Study of the Skin of the Dorsal and Ventral Areas of the Flounder Boleophthalmus dussumieri (Teleostei: Oxudercidae) in Khor Musa (Northwest of the Persian Gulf) مطالعۀ بافت‌‌شناسی پوست نواحی پشتی و شکمی گلخورک Boleophthalmus dussumieri (Teleostei: Oxudercidae) در خور موسی (شمال غربی خلیج فارس) 25 36 26943 10.22108/tbj.2022.133463.1198 EN Fahime Saberi Ph. D. Department of Biology, Faculty of Science, Razi University, Kermanshah, Iran. fahime.saberi.1991@gmail.com Ahmad Gharzi Associate Professor, Department of Biology, Faculty of Science, Razi University, Kermanshah, Iran. Ashraf Jazayeri Assistant Professor, Department of Biology, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran. Vahid Akmali Associate Professor, Department of Biology, Faculty of Science, Razi University, Kermanshah, Iran. Khosro Chehri Assistant Professor, Department of Biology, Faculty of Science, Razi University, Kermanshah, Iran. Journal Article 2022 05 01 Mudskippers, belonging to the Oxudercidae family, are amphibious creatures capable of spending extended periods out of water. In this study, Boleophthalmus dussumieri was sampled from Petroshimi and Jafari stations. For histological analysis, samples (3 males and females from each station) were anesthetized and fixed in Boyne's fixative solution, adhering to biological ethical principles. Subsequent tissue sectioning and H&E staining were performed. Observations made using a light microscope revealed that the epidermis consists of a stratified epithelium comprising three cell layers. The skin's dermis contained thick collagen fibers and numerous blood capillaries. In some regions, protrusions from the dermis extended into the epidermis, termed dermal protrusions. A significant difference was observed in the epidermis layer's thickness between males and females, measuring 87.97 microns in females and 74.32 microns in males. Considering the amphibious lifestyle of mudskippers, in species that are more hydrophilic, the upper and middle parts of the body, typically more exposed to air, exhibit shorter diffusion distances. Thus, it is likely that air absorption through the skin in B. dussumieri occurs predominantly in the upper body rather than in the lower parts or appendages. Introduction The term mudskipper refers to four genera - Periophthalmus, Periophthalmodon, Boleophthalmus, and Scartelaos - collectively known as fish-amphibians, each exhibiting varying degrees of adaptation to terrestrial conditions. Boleophthalmus dussumieri, a member of the Oxudercidae family, is distributed along the coasts of the Oman Sea and the Persian Gulf. Mudskippers are capable of breathing through their skin, the lining of the mouth (mucous membrane), and throat. This mode of respiration is viable when their skin is moist and wet. This type of breathing, similar to that in amphibians, is known as cutaneous or skin respiration. Various studies have been conducted on this group of fish in East Asia. To further explore this topic, the present study aimed to perform a histological investigation of the dorsal and ventral surfaces of B. dussumieri, focusing on its role in respiration. Materials and Methods In this study, several specimens of B. dussumieri were captured alive by hand during the spring season of 2020-2021 from Khor Mahshahr, located in the northwest of the Persian Gulf. The morphological index traits were verified using a reliable identification key. A 1 x 1 cm section of skin was incised from both the back and abdomen of each specimen. Conventional methods for tissue section preparation were employed. Subsequently, 5 μm thick sections were prepared and subjected to general hematoxylin-eosin (H&E) staining. For histometric studies, an optical microscope equipped with a Dino-Lite digital lens and Image J software was utilized. The measurement results were analyzed using SPSS 20 software. Results and Conclusions Microscopic observations revealed that the epidermis of B. dussumieri consists of a stratified epithelium with three cell layers: the surface layer, the middle layer, and the reproductive layer. The surface layer of the epidermis comprised several layers of flat, squamous cells, along with a significant number of intraepithelial blood capillaries near the body surface. Nucleated red blood cells in these capillaries were located close to the fish's surface. The middle layer of the epidermis contained several layers of spherical to polyhedral cells with a central nucleus, referred to as vesicular cells. The basal or germ layer consisted of several rows of cubic cells with a spherical nucleus. Additionally, the histological study indicated that the skin's dermis had thick collagen fibers. A comparison of the epidermis layer's thickness revealed a significant difference between males and females. The epidermis was thicker in females than in males. Furthermore, a significant difference was observed in the epidermis thickness between the dorsal and ventral surfaces in both sexes. However, there was no significant difference in diffusion distance between the sexes, although the average diffusion distance was smaller in females compared to males. In males, the diffusion distance varied greatly between the dorsal and ventral surfaces, whereas in females, it was significantly different only at the abdominal level. The basal layer thickness difference was significant in both areas. The thickness of the middle layer was greater in females than in males. Finally, a comparison of the external layer indicated that its thickness on the abdominal part of males differed significantly from that on the abdominal surface. The tissue section comparison in B. dussumieri populations suggested that adaptation to dry conditions affected the thickness and structure of the epidermis, as well as the distribution, abundance, and function of the capillaries within it. The presence of skin protrusions in B. dussumieri reduced the outer layer of the epidermis. This finding aligns with other studies where dermal protrusions were observed in all Boleophthalmus and Scartelaos genera within the epidermis structure. Given the amphibious lifestyle of these gill-feeding fishes, species that are more hydrophilic typically have smaller diffusion distances in the upper and middle body parts, which are often exposed to air. The genera Periophthalmus and Periophthalmodon, known for direct skin respiration through air, are considered air-breathing fish. Adaptations such as a thicker epidermis, well-developed vascularization, fewer blood capillaries, and reduced diffusion distance may facilitate dermal respiration, enabling survival in poorly oxygenated water during dry seasons. Funding This study was funded by the Department of Biology, Faculty of Sciences, Razi University, Kermanshah, Iran.

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