A comparative study on vascularization and the structure of the epidermis of an amphibious mudskipper fish,Scartelaos gigas(Gobiidae, Teleostei), on different parts of the body and the appendages

Abstract

Summary Epidermal structure of the amphibious mudskipper, Scartelaos gigas (Gobiidae), was investigated in relation to their terrestrial adaptation whereby a histological study on the epidermis of 15 regions including nine body regions, five fins and the sucking disc was carried out. The structure of the epidermis consists of three layers: an outermost layer with polygonal cells or rather flattened cells, small cells and mucous cells; a thick middle layer with voluminous cells swollen by epidermal cells; and the stratum germinativum. A dermal bulge was located at each apical area of the epidermis of almost all body regions, but was not existent in the operculum and the appendages, including none of the fins or the sucking disc. In the epidermis of the body regions, the dermal bulges had numerous dermal capillaries just beneath the stratum germinativum. By contrast, the appendages never had dermal capillaries due to the absence of the dermal bulge. Based on these results, the cutaneous air uptake in S. gigas would seem to be more effective in the upper body regions that are most often exposed to air than in the lower body regions, however, cutaneous air uptake is not likely to occur in the appendages.

Comparative Transcriptomic Analysis of Regenerated Skins Provides Insights into Cutaneous Air-Breathing Formation in Fish

“…The middle layer of cutaneous epidermis in air-breathing fish is composed mostly of a variety of epithelial cells with oxygen carrying capacity [ 19 ], however, this layer of loach was mainly composed of multi-layered swollen cells, which were bulky and vacuolated. Similar structures occurred in the middle layer of amphibious skin [ 35 ]. The multi-layered structure possibly played a role of a water-blocking barrier to keep the skin moist when exposed to the air for a long time [ 22 ].…”

“…The multi-layered structure possibly played a role of a water-blocking barrier to keep the skin moist when exposed to the air for a long time [ 22 ]. In many fish species with cutaneous respiration, such as mudskipper ( Periophthalmus cantonensis ), abundant micro-vessels were also detected in the epidermis [ 35 ]. Two “trauma models” of skin resection in loach (cutaneous air-breathing fish) and yellow catfish (non-cutaneous air-breathing fish) were uniquely adopted in exploration to the mechanism of fish cutaneous accessory respiration.…”

“…After the cutaneous trauma occurs, it is repaired in three stages: inflammation, tissue formation, and tissue remodeling [ 36 ], among which angiogenesis and vascularization are important factors in wound healing [ 37 ]. The histological evidence indicated that the respiratory function of fish skin lies on the well vascularization in skin [ 35 , 38 , 39 , 40 ]. The original and regenerated skins of these two fish species were investigated by transcriptome analyses.…”

A review about fish walking on land

“…In comparison, terrestrial adaptations were favoured more at odds with their amphibious lifestyle (Low et al 1988). Since mudskippers appear to change the way their skin breathes, their epidermis and skin layers have been studied in detail (Beon et al 2012). They adapt towards terrestrial lifestyle by secreting mucus, and their head containing dense capillary network assists cutaneous respiration (Jie et al 2003).…”

Morphology of the respiratory vasculature of the mudskipper Boleophthalmus pectinirostris (Gobiidae: Oxudercinae)

“…The respiratory organs of mudskippers consist of the bucco‐opercular cavity (the space in the buccal, pharyngeal, and opercular cavities combined), gills, and skin, unlike specialized air‐breathing organs seen in various aquatic air‐breathing fishes (Ishimatsu, 2017). The morphology and histology of the respiratory organs of mudskippers have been relatively well investigated (Al‐Kadhomiy & Hughes, 1988; Beon et al, 2013; Mazlan et al, 2006; Park et al, 2003; Park et al, 2006; Schöttle, 1931; Suzuki, 1992; Yokoya & Tamura, 1992; Zhang et al, 2000; Zhang et al, 2003), whereas the circulatory system of mudskippers has received little attention. A notable exception is the study by Elfriede Schöttle, who reported on the gross and fine morphology of the circulatory system of five species of mudskippers (Ishimatsu & Ishimatsu, 2021; Schöttle, 1931).…”