Abstract
The process of recovery from bacterial gill disease, which is characterized by a hyperplasia of the gill epithelium, was examined by transmission and scanning electron microscopy. An attempt to effect recovery from the disease was made by immersing naturally infected rainbow trout fingerlings for 1min in a 5% solution of sodium chloride. This treatment was very effective for the removal of bacterial cells and subsequent recovery. The removal resulted in the degeneration of epithelial and chloride cells in the outermost layer and the subsequent breakdown or exfoliation from the surface of the hyperplastic epithelium. In the superficial layers of epithelial cells in hyperplastic lesions, electron lucent or pale granules (275nm in average diameter) appeared singly or in groups; these are formed by Golgi complexes. The opening of the granules may accelerate the exfoliation of degenerating cells from the hyperplastic epithelium. These processes resulted in the complete recovery of the gill epithelium. A cytoplasmic “cutting-away” or “fragmentation” of epithelial and chloride cells was observed in the deep interior of the lesions.
