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In this sludy, the actiological agent and histopathological changes of a infectious diseases induced high mortality in our Faculty Rainbow Trout Hatchery Unite fish (2-3 months old) located in Sapanca were investigated.
Bacieriological inoculations were made from kidney, liver and spleen to Tryptic Soy Agar (TSA) Irom ıhe intected fish visceral organs. The bacterial colonies were obtained only from kidney inoculation after 5 days period incubation at 20*C. The isolate were comprised motile Gram negative rod shaped bacteria those strictly oxidative by the O/F glucose test, cytocrome oxidase positive and produced fluoresce under ultraviolet light and identified as Pseudomonas fluorescein. Affected fish showed darkening of the skin, fin or tail rot, haemorrhagic lesions on the skin and the base of the fins, anorexia, exophtalmia. Main histopathological changes were localized in the interstitial haemopoietic tissue of kidney and in the muscle cells of the underlying dermis. In addition to this findings diffuse oedema among the liver cells and focal necrosis in the liver and kidney tubul epithelium cells, necrosis in the gill epithelium and haemorrhagie were also seen.