Aquaculture remains one of the fastest-growing food-producing sectors and is set to play a key role in meeting the rising demand for fishery products that consider one of the cheapest sources of protein, Nile tilapia is the most economically important Freshwater Fish in Abbassa Farms and the most popular in Egypt. A total number of 100 randomly collected O. niloticus fish of different stages and different weights were obtained alive taken to lab. of fish health and management department in central lab for Aquaculture Research (El-Abbasssa), Sharkia, during the period from December 2018 to May 2019. The fish were subjected to clinical, post-mortem examination, Fungal isolation and identification revealed Saprolegnia sp., Penicillium sp., Rhodotorulla, Aspergillus niger., Fusarium sp., Aspergillus Ochraceus, Aspergillus flavus, Aspergillus tamari, Absidia sp and Aspergillus versicolor sp.
And histopathological for pathogenic fungus (Saprolegnia sp.), tissue specimens were taken from suspected lesions for Histopathological examination and showed severe hyperplasia of epithelial cell covering of secondary lamella of gills, alternative area of hyperplasia of sloughing of epidermis, increase number of mucus secreting cell; severe congestion of hebatoportal vein and central vein in liver; increase numbers of MMCs in spleen; condensation of glomuler tubules with edema in Bowman's capsule in kidney.