A comparative study of the skin, based on the micro-anatomical investigation of skin fragments taken from a specific region of the body, has been made of three air-breathing fishes, namely, Heteropneustes fossilis, Amphipnous cuchia and Mastacembelus pancalus.
On the basis of their structure and histochemical nature, five types of skin glands have been distinguished in the epidermis of these fishes.
The relative thickness of the epidermis (A. cuchia–119 μm (average value), H. fossilis– 98 μm (average value), M. pancalus–34 μm (average value)) and its vascularization has been considered and compared with other fishes and amphibians. The possibilities of cutaneous respiration in these air-breathing fishes has been discussed.
The presence of a well-defined lymphatic system, comprising a series of lymph spaces containing small lymphocytes, in the stratum germinativum layer of the epidermis of these fishes has been established.
The stratum laxum layer of the dermis in Amphipnous is characterized by the presence of definite areas containing “Substantia amorpha” having acidic mucopolysaccharides which may be related with the amphibious habit of the fishes. This is an adaptation against desiccation similar to that found in the Anura. In Mastacembelus elliptical areas of the stratum laxum penetrate into the epidermis thus making these areas of the epidermis considerably thin (about 7 μm) for cutaneous respiration.
There is an inverse relationship between the thickness of the stratum compactum and squamation.