Clinical signs and post mortem lesions were recorded on a large number of Nile tilapia, O.niloticus, specimens. Bacterial isolates were characterized to confirm the presence of Aeromonas Hydrophila. Our results showed that prevalence of A. hydrophila infection was higher in cultured fish during the summer season than in wild fish. The observed clinical signs in the examined fish suffering from Motile Aeromonas Septicemia (MAS) were varied from septicemia, ascitis, erosion, ulceration, detachment of scale and exophthalmia. The postmortem findings varied from congestion to focal lesions in the liver, spleen, and kidney. We collected 25 isolates of A. hydrophila from sterile extra-intestinal organs of naturally infected Nile tilapia, O. niloticus.
There was a pronounced variation in both the biochemical and enzymatic profiles within the motile aeromonas species. Variation was evident in the hemolytic activity. Similarly, there was variation in pathogenicity among the 25 isolates of A. hydrophila. The relation between pathogenicity and the biochemical activity is discussed.