الفهرس 
Abstract
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Abstract
The present results could be concluded in the following:
1. Streptococcosis was recorded in Nile tilapia at El-Ibrahemia lake in Upper Egypt.
2. The prevalence of infection in nature was found to be 10% allover the tested period, where this illustrated the danger of that disease.
3. This disease was found to be more prevalent in summer than in winter.
4. The disease caused, more or less, a considerable mortalities indicating that it is a devastating disease threatening Nile tilapia populations both in natural resources and aquaculture.
5. It was found that the Kidney represents the best organs for the isolation of the Streptococcus faecium at any time of infection, where the microorganisms were detected with higher numbers than the other organs.
6. The presence of the causative agent in the water allover the year represents a continuos source of infection.
7. As the identification of the fish and water isolates revealed that they were the same, this may confirms the concept of the discharge of that microorganisms from the diseased fish as a source of the diseases. Hence, isolation of infected fish from the fish stock is an important measure for the disease control.
8. The isolated Streptococcus faecium remained viable for up to 6 days in distilled water. As such, there is a potential for the pathogen to remain viable in the more nutritive mud and water for long periods.
9. The antibiotic sensitivity tests revealed that Streptococcus faecium is sensitive to many antibiotics, where oxytetracycline and doxycycline proved to be the most effective antibiotics against this microorganisms.
10. Further investigations should be done to produce a polyvalent commercial vaccine.