• Korean Journal of Veterinary Research
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• v.32 no.3
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• pp.381-387
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• 1992

Gill epithelia of normal rainbow trout fingerlings and abnormal ones suffering bacterial gill disease by experimental infection were examined by transmitting electron microscopy (TEM) and scanning electron microscopy (SEM). TEM observations revealed that Flavobacterium branchiophila consisted of slender rods measuring 0.5 by 5 to $8{\mu}m$, and they had which were long, thin, flexible filaments measuring approximately 4 nm by $1{\mu}m$, and packed together to organize into bundles. Morphological alterations of the diseased epithelia started at hypertrophy of the lamellar epithelium. F branchiophila attached to the gill surface of infected fish through pili with a regular distance, and did not invade into gill tissue. In SEM observations, normal surface ultrastructure of epithelial cell in the outermost layer were characterized by a typical labyrinth-like structure branching and anastomosing microridges on the cell surface. Hyperplastic lesions in experimentally infected gill were most serious at near the tips. Each filament exhibited a club-like, and fusion between the filaments was sometimes observed at their tips. On the surface of gill filaments, thread-like bacterial cells attached and were entangled. The bacterial cells almost covered the surface. After immersion in 5 % NaCl, the cell of F branchiophila, however, appeared to be indeterminate shape.