Observation of the Skin Histology of Thamnaconus septentrionalis

Fish skin is a multipurpose tissue with important functions—protection, perception, and hormone metabolism—in the fish body. As a byproduct of fish processing, it can be used as a material for extracting collagen, making leather, and related pathological research. However, there have been few reports on the tissue structure of fish skin. This study aimed to analyze the structural characteristics of Thamnaconus septentrionalis fish skin in order to provide a reference for the utilization of its resources. Six T. septentrionalis samples were selected and their skins were observed using frozen sectioning, skeletal, hematoxylin & eosin (H & E), Periodic acid-Schiff (PAS), Masson, Van Gieson (VG) staining, and scanning electron microscopy. The images obtained by slice scanning were analyzed using SlideViewer (3DHISTECH), ImageJ, and Photoshop software. The SEM images were analyzed using ImageJ and Photoshop software. SPSS25.0 software was used to analyze the data of epidermal and squamous layers, conical bone bulge, basal layer, and dermis thicknesses. The results showed that the histological structure of the skin comprised four parts: epidermis, scale layer, dermis, and subcutaneous tissue. The thickness of the epidermal layer was (26.81±7.48) μm. This layer was mainly composed of epithelial and basal cells but also contained a large number of mucus cells. The scale layer consisted of the spine of conical bone and a substrate. The thickness of this layer was (22.49±5.19) μm, and there were two to four rows of the spine of conical bone with different diameters, different bending degrees at the top, and a height of (257.13±10.41) μm unevenly distributed on the base plate. The average thickness of the dermis was (176.97±21.11) μm, and the dermis thickness of the head was lower than that of the middle part of the body, but higher than that of the tail, mainly composed of collagen fiber. The subcutaneous tissue layer was mainly comprised of collagen fibers and non-fibrous stroma. In this study, the histological pattern of the skin of T. septentrionalis was mapped according to its characteristics, providing valuable information for fish skin resource usage.