Histopathological studies on the repair of the excised skin wounds of the air-breathing scalyfish Channa striata (Bloch)

Regeneration and repair of excised wounds in the skin of the scalyfish Chan na striata have been studied. The present investigation revealed that regen eration processes in fishes vary greatly from that of mammals. Following in jury in the skin of C. striata, the free borders of the wounds retract and within an hour, the areas surrounding the wound become very dark. The norma l shade is however, restored after 24 h. A mass movement of the epidermis t owards the wound gap starts at about 2 h, which results in the epithelializ ation of the wound gap within 4 to 6 h. This is in contrast to dry mammalia n skin where the granulation tissue appears first and the epithelialization takes place quite late and new epithelial cells are produced due to mitoti c division of the cells of the stratum germinativum of the epidermis. Subse quently the thickness of the epidermis covering the wound gap in C. striata rapidly increases due to hyperplasia of the polygonal epithelial cells. La ter, the epidermis gets equipped with numerous sac-like goblet mucous cells which lay a copious amount of slime on the newly regenerated epidermis for protecting the underlying damaged tissue components. At about 16 h, numero us ionocytes appear in the epidermis covering the wound gap, playing active roles in maintaining the normal osmotic equilibrium. The epidermis gradual ly becomes thinner with the development of scales in the underlying tissues and appears normal by 20 days. The denuded muscle bundles in the wound gap start disintegrating soon (30 min) after the lesions are made and by 4-5 d ays are replaced by the granulation tissue. With the initiation of disinteg ration of the denuded muscle bundles, an amorphous PAS positive substance a ppears in the wound gap, the quantity of which gradually increases and reac hes its maximum within 6-10 h when the muscle bundles show maximum vacuoliz ation and attenuation. The process of fibre formation in the granulation ti ssue begins at about 5 days; simultaneously myoblasts appear at the level o f old muscle bundles and start differentiating into new muscle fibres. The appearance of melanophores and leukocytes in the regenerating tissues has b een correlated with the local defence mechanism of the newly formed epiderm is. The pigment cells also appear in the sub-epidermal granulation tissue. Later, the outer layer of the granulation tissue gets differentiated into s tratum laxum with the formation of numerous fat cells, the scales, and the inner layer into stratum compactum which shows the appearance of compactly arranged connective tissue fibres and the fibroblasts. Differentiation of f at cells also takes place at the level of the subcutis. The wounds get comp letely repaired within 35 days and unlike in mammals leave no scar or scab of the wound on the surface of the skin.