Skin Characteristics and Organization of the Air-breathing Fish, Alticus kirkii (Gnther, 1868) along Different Body Regions</B>

Alticus kirkii is an air-breathing fish inhabiting the intertidal zone of the Red Sea. The study aimed to determine the role of the skin of this species in air-breathing in terms of histological characteristics of the Epidermis and its Thickness (EPT), blood Capillary Number (CN), Mucous Cell density (MC) and the Diffusion Distances (DD) along ten different body regions of A. kirkii and to assess which region of the skin is most effective. The basic statistics of the measured parameters and the patterns of variations were estimated and analyzed using one way analysis of variance. The relationships between skin parameters were revealed by cluster analysis through different skin body regions and vice versa. The principle structure of skin is evident on different body regions with significant variability (p<0.05) in epidermal thickness (1.08 to 3.94 m), diffusion distance (0.89 to 1.67 m), mucous cell number (0 to 5.55 per 25 m length) and blood capillary density (0 to 10.55 per 25 m length). This variability refers to the contribution role of each region in air-breathing; the skin on the ventral side which is easily immersed in water or soft mud during amphibious life has no role in this concern. The epidermal thickness in the different body regions was inversely associated (p<0.05) with CN, DD and MC (R = -0.94, -0.55 and -0.62, respectively) and is isolated into a single cluster. CN significantly correlates with MC (R = 0.65) (p<0.05) and insignificantly with DD (R = 0.47) (p<0.05). These three parameters are classified into one cluster with subcluster of CN and MC. Based on EPT, CN, MC and DD, the ten skin regions are classified into two main clusters, one includes the ventral head and pelvic fin regions and the other cluster includes the rest of skin regions which are more adapted to air-breathing; the crest skin is isolated in a separate subcluster. In conclusion, the high vascularization, numerous mucous cells and the thinness of the epidermis of A. kirkii may be ones of the cutaneous adaptations that permit enhanced perfusion during aerial exposure. Accordingly, A. kirkiii is more adapted to cutaneous respiration as a dual respiratory system.