Summary
The present work aimed at throwing some light on histological, ultrastructural and immunohistochemical structure of the skin of catfish. To achieve such purpose, a number of 30 specimens from head, trunk and tail of mature catfish were collected during different seasons which were subjected to different investigations. For light microscopy, specimens were fixed in 10% buffered neutral formalin and processed until paraffin sections were prepared. In addition, specimens were fixed in 2.5 and 5 % glutaraldehyde and processed for scanning and transmission electron microscope examination, respectively. Imunohistochemical study was carried out using BAX.
The skin was consists of three layers, epidermis, dermis and hypodermis. The epidermis was consists of stratified squamous epithelium containing malpighian, mucous cells and club cells (alarm cells). The malpighian cell is the main component of the epidermis of fish skin. In the basal layer of epidermis, they appeared as columnar cells, while in the superficial layer the cells became flat. The mucous cells were varied from round to goblet shape with basal basophilic nucleus and acidophilic cytoplasm. They distributed at middle and superficial layer of the epidermis. Some of mucous cells open to the outer surface of the skin and release mucous secretion which form mucus layer. The club cells had different shapes; round, oval and elongated with spherical central basophilic nucleus. They located at the middle layer of epidermis.
The dermis contained stratum spongiosum or adiposum depending upon body region and seasonal variation beside stratum compactum. Stratum compactum composed of bundles of collagen fibers. Stratum spongiosum comprised of loose connective tissue contain collagen, reticular fibers, blood, nerve vessels and melanocytes. Stratum adiposum composed of upper layer of connective tissue contain melanocytes and lower layer of clusters of adipose cells which were surrounded by capsule of connective tissue. Hypodermis comprised of loose connective tissue containing adipose cells.
SEM investigation showed elevations of epidermal cells which contain openings of mucous cells. Mucous cells showed lobulated elevations, while club cells showed large elevations. The dermis contained bundles of collagen fibers.
TEM investigation showed a stratified epithelium of epidermis containing the mucous and club cells. Mucous cells varied from oval to goblet shape with basal, oval or spherical nucleus, mucous granules filling apical part of the cell and microvilli on the free border of the cell. Club cells have oval shape with spherical, central one or two nuclei with prominent nucleolus. Dermis comprised of collagen fiberils in longitudinal and cross sections with melanocytes in between.
Immunohistochemical study revealed that the epidermal reacted positively with BAX and club cells showed faint reaction, while the mucous cells show a negative reaction.
During different seasons, it was found that the skin of head during summer is highly folded than that of the winter and autumn. The head epidermis was composed of stratified squamous epithelium containing mucous cells more than that of the club cells during summer, while club cells more than that of the mucous cells during autumn and winter. The dermis of head consisted of stratum adiposum and stratum compactum.
The epidermis of trunk during summer, ventral trunk during autumn and winter composed of stratified squamous epithelium containing mucous cells more than that of the club cells, while the epidermis of the dorsal trunk during autumn contained club cells more than that of the mucous cells. The dermis of dorsal trunk during summer and winter consisted of stratum spongiosum and stratum compactum .On the other hand, the dermis of trunk during autumn and ventral trunk during summer and winter consisted of stratum adiposum and stratum compactum. The dermis of dorsal trunk contains numerous melanocytes than that of ventral trunk
The skin of tail is thinner than that of head. The skin of tail during autumn is thinner than the skin of head in this season and thinner than the tail skin in winter and summer.The epidermis during summer appeared as a thin layer of stratified squamous epithelium containing mucous cells more numerous than that of autumn and winter, while in autumn and winter, club cells more than that of the mucous cell. The dermis consisted of stratum spongiosum and stratum compactum.
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