Sixty fishes of common carp (Cyprinus carpio) were obtained from the farm of Marine Science Center, University of Basrah. These fishes were divided into six groups (10 fishes/20 liters aquaria). One of these groups was injected intraperitoneally (I.P.) with an isolate of non-hemolytic Streptococcus at a concentration of 1 X 104 CFU/ ml. The other two groups were inoculated with 2.5 X 107 CFU/ ml of the same isolate via water pollution, one with and the other without skin abrasion. The other three groups were left as control and the experimental period was 35 days. The mortality rate was 100% in the I.P. inoculated group during the first week of the experiment, while nil in the other groups. The most important clinical signs of I.P. inoculated fishes were corneal opacity, erratic swimming, hemorrhage on the body surface especially in the base of fins. The other groups did not show any signs. Postmortem examination revealed general pathological changes of septicemia. Hemorrhage in the peritoneum, liver, kidney, gills, intestine, heart and brain of affected fishes. The kidneys were moderately swollen, enlarged spleen, pale liver as well as inflammation was noticed around kidney, heart and eye. Hyperplasia and necrosis of gills have been seen. Ascetic was also seen, while internal examination of other groups which were inoculated by aquarium with and without skin abrasion as well as their control groups did not reveal any obvious postmortem changes during the experiment. Microscopic examination revealed edema and inflammation of brain, eye exhibited hemorrhage and inflammatory cells infiltration, thickening of epithelial tissue of gills followed by necrosis and sloughing of these
tissues. Degeneration and inflammation of myocytes and cardiocytes. Hydropic and fatty degeneration, congestion, hemorrhage and necrosis of hepatic cells. Glomerulonephritis and.
depletion of hemopoitic tissue in kidney