الفهرس 
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Abstract
In our investigation, a total number of 120 freshwater fish samples of different sizes and weights namely, (60 each of Oreochromis niloticus and Common carp Cyprinus carpio) were obtained f The importance of fungal diseases in freshwater fish not stopped only for incidence of mortalities but also as economic importance such as decrease growth rate, hatchability in chronic infection or by mycotoxins production by contaminated fungus in case of bad storage feed. from different 4 private freshwater fish farms at Domitte, Port-said, El-Behera and Kafr El Sheikh governorates, Egypt (15 samples / each species from each farm) were transmitted to the laboratory of the Department of Poultry and Fish diseases, faculty of Veterinary Medicine, Alexandria University. The freshly dead fish specimens were subjected to full clinical signs, postmortem (PM) lesions and mycological examination as well as advanced diagnosis of isolated and identified fungus by Polymerase chain reaction (PCR) in addition to histopathological study. Measurement of water qualities along the period of survey in all farms were carried out. The results revealed that:- 1.The examined naturally infected fish showed, scales detachment with ulceration at different parts of the body, skin discoloration (O. niloticus), fins erosion specially dorsal and caudal fins, and the fish appear biting as well as complete sloughing of gill lamellae .While, clinically diseased C. carpio showing, signs of skin darkening, prediction on the lateral surfacefin erosion specially the dorsal fin, congestion or predication on the operculum and haemorrhage on the anal opening. 2. The characteristics alternative congested area with the pale necrotic areas on the affected gills (marbling appearance) was predominant in the most examined cases in p.m. examined fishes. 3. The incidence of infections in different fish species O. niloticus and C. carpio in four farms revealed that the percentage of infection were high in Kafr El Sheikh followed by El-Behera governorates, while the Domitte and Port-said governorates were lowest in the incidence of infection in both types of examined fish. 4. The water quality in all farms (4 farms) recorded that fish suffering from an environmental stress, such as low pH (5.8 to 6.5), low dissolved oxygen. High organic loads, high nitrate, nitrite levels, and unionized ammonia (0.19 to 0.41mg. /L.) .The data also documented that the salinity is ranged between 1 ppt to 3 ppt. 5. The highly prevalent of Branchiomyces spp. in examined C. carpio, where 36 isolates were recorded from 52 infected fish. On the other hand the 20 isolates recorded from 39 infected O. niloticus. The percentage of infection in both C. carpio and O. niloticus was 60% and 33.33 % respectively, from total of 56 isolates observed from all examined gills. 6. The morphological characteristics of the isolated fungi were found to have the same characters of Br. demigrans 7. The result of diagnosis of fungal materials of Br. demigrans by PCR amplification revealed that the isolates were characterized by studying the sequencing of the internal transcribed spacer of nuclear ribosomal DNA (ITS1+5.8S+ITS2). The results indicate the sequence comparisons of two ITS nuclear DNA for species identification. Results indicate that our isolates corresponded to the species Br. demigrans. 8. The mortality percentage for Br. demigrans was increased by induction of all predisposing factors as low pH value, high organic matter, high ammonia level and high water temperature. The highest mortality percentage was noticed in group (Infected fish + high unionized ammonia level, 0.32 mg. /L) where reach to 45%. On the same manner the groups of infected fish stressed by low pH level (6.2), high organic matter level (4.3 mg./L) and high Temperature degree (28.5 oC) as well as without continuous water exchange the mortality percentage were also high and recorded by 40% in all above mentioned groups. The second rank of the mortality percentage was recorded in groups (infected fish + Permissible limit of unionized ammonia level (0.01 mg. /L) and infected fish + normal temperature degree 25 oC) where it reach to 20% respectively. The lowest mortality percentage was reported in groups (Infected fish + with continuous water exchange, Non-Infected fish + without continuous water exchange, infected fish + Permissible limit of pH (7.9) and Infected fish + Permissible limit of organic matter (1.1 mg./L) where the percentage reach to 15%, 10%, 5% and 5% respectively. It worthy to be note the mortality percentage was zero in control group (non-Infected + with continuous water exchange). 8.1. The results of WBCs counts, RBCs counts and Hb% among different groups during experimental infection by Br. demigrans in presence of predisposing factors revealed that the all infected groups associated with stress factors were suffered from severe decrease of WBCs counts, RBCs counts and hemoglobin percentage. The data also, documented that the most affected groups were the (Infected fish + high organic matter level (4.3 mg. /L) and Infected fish + high unionized ammonia level (0.32 mg. /L) followed by Infected fish + high temperature degree (28.5 oC) and Infected fish + without continuous water exchange. 8.2. It was notice that there was decreasing in phagocytic activity and phagocytic index in the groups infected with Br.demigrans associated with predisposing factors(without water exchange) along the period of experiment than the infected without predisposing factors(with water exchange) . 8.3. Serum total proteins and globulin were significantly dropped in the groups infected with Br. demigrans associated with predisposing factors along the period of experiment and more than the infected without predisposing factors. The total proteins and globulin in groups infected with Br. demigrans associated with predisposing factors namely; low pH, high organic matter, high unionized ammonia and high temperature were (4.33±0.33, 4.33±0.33, 3.00±0.58, 4.67±0.33 and 1.67±0.33, 1.67±0.33, 0.87±0.33, 2.33±0.33 respectively).It worthy to be note that total proteins, and globulin in infected groups with Br. demigrans without predisposing factors (5.00±0.58, 5.33±0.33, 5.67±0.67, 6.10±0.15 and 2.33±0.33, 2.67±0.33, 2.33±0.33, 5.10±0.44 respectively). 8.4. The serum lysozyme was significantly decreased progressively in the groups infected with Br. demigrans associated with predisposing factors namely; low pH, high organic matter, high unionized ammonia and high temperature. The serum lysozyme concentration of the fish infected with Br. demigrans associated with predisposing factors namely; low pH, high organic matter, high unionized ammonia and high temperature were 0.02±0.00, 0.011±0.00, 0.011±0.00 and 0.036±0.00 respectively. 9. The effect of different chemicals on the infected C. carpio with branchiomycosis associated with predisposing factors revealed that the potassium permanganate gave the most effective result when compared with the copper sulphate, formalin and even when continuous exchange of the water. 10. The histopathological results of gill of C. carpio associated by induction of infection by Br. demigrans associated with applied of all predisposing factors recorded under field condition as low pH value, high organic matter, high ammonia level and high water temperature showing; dilation and congestion of blood vessels of primary lamellar epithelium, aneurism, swelling of secondary lamellae as well as telangiectasis , degenerative changes, necrosis and oedema as well as the blood capillaries became large cysts , hematomas , curling of secondary lamellae , degenerative and necrotic changes in the epithelium of gill filaments and secondary lamellae and edema as well as hyperplasia in secondary lamellae ,complete destruction and proliferation in the epithelium of gill filament.