الفهرس 
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Abstract
This study involved the collection of 200 clinically and macroscopically diseased Common carp from the Central Laboratory for Aquaculture Research in Abbassa, Sharkia Governorate. All fish were subjected to bacteriological and parasitological as well as pathological examinations. Bacterial diseases diagnosis was confirmed via experimental infection of healthy fish by using the isolated bacteria from the naturally infected carp. Out of these examined Common carp, 170 common carp were infected by bacteria with a prevalence of 85%, 20 fish were infected by parasites with a prevalence of 10% and 10 Common carp showed mixed bacterial and parasitic infection with a prevalence of 5%. Experimentally, the mortality in mixed infection represented 96%, while in A. hydrophila and Ps. Jluorescens were 88% and 76%, respectively. The Common carp, which naturally infected by A. hydrophila revealed loss of appetite, exophthalmia and abdominal distension clinically. Congestion of gills and most of internal organs inacroscopically. While microscopic~lly, in the gills some of secondary lamellae revealed epithelial hyperplasia while others were desquamated. Pericarditis, muscular edema and degeneration were seen with hepatic and pancreatic degeneration. Catarrhal enteritis and renal tubular nephrosis were commonly noticed. The swim bladder exhibited sloughing of the epithelial lining with congestion, edema, hemorrhage and mononuclear cells in muscularis mucosa, also melanomacrophage cells aggregations in the subepithelial tissue were observed. The experimentally infected Common carp by A. hydrophila revealed similar picture to naturally infected cases. In addition to, severe swim bladder lesions represented by shrinkage of the posterior chamber with marked congestion, necrosis, hemorrhage and mononuclear cells infiltration of tile swim bladder wall. Moreover, hemopericardium and hemoperitoneum, were detected. In case of mixed infection by bacteria and parasites, we isolated A. hdroph i/a from Common carp infected with encysted metacercariae in the muscle Microscopically, the muscles showed intennuscular edema and focal hyaline degeneration as well as zenker’s necrosis. The encysted metacercariae between the muscle bundle surrounded by fibrous capsule, mononuclear leukocytes cells and melanomacrophage cells. In other cases, we isolated A. hydrophila from Common carp infected by plerocercoids which embedded in the hepatic parenchyma, inducing a marked pressure atrophy and necrosis in the surrounding hepatic tissues. The Common carp which naturally infected by Ps. Jinorescens clinically revealed exophthalmia, loss of balance. While Macroscopically, dark body color, abdominal distension, focal hemorrhages on the skin and congestion of most internal organs including swim bladder were evident. The swim bladdershowed congestion of posterior chamber whiie the anterior chamber became whitish gray with petechial hemorrhage. Microscopically, the gills revealed congestion, telangiectiasis of gill lamellae with epithelial hyperplasia or desquamation. Marked degeneration was evident in the liver, heart and kidneys. Enteritis, necrosis of renal melanomacrphage centers and alternative hyperplasia or depletion of renal hemopoietic tissues with edema and mononuclear leukocytic infiltration were seen. The experimentally infected Common carp by Ps. Jluorescens revealed similar picture to those of naturally infected cases with marked petechiae and congestion of most internal organs especially the swim bladder, which exhibited focal heinonhage and thickened cloudy wall. While microscopically, edema, congestion and hemorrhage were evident in most internal organs, including the swim bladder which exhibited focal hyalinization in the muscle layer. Necrosis of hemopoietic tissues with rupture of melanomacrophage centers in spleen and kidneys were observed. The Common carp which naturally infected by mixed A. hydrophila and Ps. fluorescens clinically revealed poor appetite, exophthalmia, loss of equilibrium and emaciation, while niacroscopically fin rot, congestion of gills and petechial hemorrhage on the surface of the liver, kidney, spleen as well as swim bladder were noticed. The intestine contained bloody exudate and the gall bladder distended with greenish bile. Microscopically the gills showed desquamation of primary and secondary lamellae with telangiectiasis as well as edema and hemorrhage in the primary lamellae. The heart showed marked pericarditis while the myocardium revealed edema and Zenlcer’s necrosis with mononuclear leukocytes. The liver and kidneys revealed vacuolar degeneration with nuclear pylcnosis in hepatic and renal cells. Necrosis of melanomacrophages, interstitial edema and focal depletion of hemopoietic tissues were noticed. The pancreatic aeini were edematous and suffered degeneration mid/or necrosis of most pancreatic acini with mononuclear leukocytic infiltration. The intestine exhibited mucinous, hemorrhage with round cells and focal epithelial cells desquamation in its lumen. The swim bladder showed necrosis and sloughing to the epithelial cells with round cells infiltration as well as edema and proliferation of some mnelanomnacrophage. The muscular layer was edematous with focal hyalinization. The experimentally infected Common carp by (A. hydrophila and Ps. Jluorescens) revealed high mortality rate during the first 3 days post inoculation. The infected carp showed loss of balance, hyperexcitation and finally loss of reflexes just prior to death. Macroscopically, The infected Common carp revealed hemorrhagic ulcer on the skin, necrotic foci in the liver. Severe congestion and hemorrhage on the internal organs including the swim bladder. Microscopically, the gills, liver, spleen, intestine and kidneys revealed similar picture to those reported in the naturally infected cases. However, focal superficial skin erosion or ulcers, necrosis of liver, kidneys and swim bladder were seen. The heart showed severe hemorrhage among the degenerated and necrosed cardiac muscle. The parasitic infection in the present study was low. The encysted inetacercariae were observed in the skeletal, cardiac muscles and kidneys of 24 case of the Common carp, encysted plerocercoids were seen in 6 case of the Common carp. No parasitic infection was recorded in the swim bladder and blood of Comon carp. Macroscopically, a small light to dark grayish cysts were noticed in the affected skeletal and cardiac muscles. Sometime, dark black pigmentation was seen in the vicinity of the parasitic cysts. Microscopically, the parasitic cyst was observed embedded in the affected skeletal and cardiac muscles inducing pressure atrophy, edema and fibrous tissue proliferation of the surrounding muscles. In other cases, fibrous connective tissue capsule was seen surrounded the cyst with mononuclear leukocytic infiltration and melanomacrophage cells aggregation. Encysted metacercaria was seen attached to the renal tissue and surrounded by connective tissue capsule. The surrounding renal tubules suffered atrophy, tubular degeneration and necrosis. Encysted plerocercoids, were seen embedded in the hepatic parenchyma and stuTounded by connective tissue capsule in addition to atrophied, degenerated and necrotic hepatopancreas. Fibrous connective tissue was seen around the plerocercoid cyst along with edema, surrounding hepatic cells as well as few mononuclear leukocytes. It could be concluded that: 1- The bacterial infections represented [lie major problem among the examined Common carp with prevalence of 85%.2- It was recorded either as a single or mixed infections; single A. h~ydroph i/a or Ps. Jluorescens and mixed infection by both were recorded with 43%, 34.5% and 7.5%, respectively. 3- Mixed A. hydroph i/a and encysted metacercariae or encysted plerocercoids were recorded with 3.5% and 1.5%, respectively. The presence of parasitic cysts in Common carp enhanced the severity of Aeromonas infection. 4- The experimental infection by A. hydroph i/a or Ps. fluorescens or both resulted 88, 76 and 96% mortalities, respectively. There mortalities due to bacteria and / or its toxins. 5- Naturally and experimentally infected Common carp by isolated bacteria showed marked lesion in the swim bladder in the form of hemorrhage with congestion and necrotizing inflammatory lesions. 6- The parasitic infections were recorded in examined Common cai-p with a prevalence of 15%. 7- Encysted metacercaria and encysted plerocercoids were the only observed parasitic stages with 12.0 and 3.0% respectively among the examined infected Common carp. 8- No parasites recorded in the swim bladder or blood of examined Common carp. 9- The effect of these parasitic cysts were mostly local on the involved organs represented by pressure atrophy, edema, degeneration and cellular infiltration.