ABSTRACT
The Nile Tilapia [Oreochromis niloticus] has been infected for four weeks with Saprolegnia. The fish showed white necrotic areas on skin which finally leads to fish death. During the time of infection, the biochemical analysis showed an obvious depletion in the protein content in both muscles and blood serum, while the liver protein content showed a fluctuated behaviour. The liver and muscle glycogen decreased irregulary. The lipids content decreased greatly in the liver while increased in muscles and blood serum. The study showed a reverse relation, allover the time period of infection between glucose level of liver on one side and glucose levels of muscle and serum on the other. The UDN disease has an economic significance since it causes the death of fish stocks in fish culture units and the River Nile