الفهرس 
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Abstract
Gram-positive bacteria cause a disease in fishes and of a considerable importance especially in the recent years. In this investigation a total number of 60 apparently healthy O.niloticus and C.carpio were used for determing the pathogenicety of S.epidermidis in addition to 600 apparently healthy O.niloticus and C.carpio to illustrate the proper effect of B.subtilis as additive to water and diet on the growth performance and blood parameters in addition to its role in compating the Staphylococcal infection.
Morphological and biochemical identification of S.epidermids was performed, then application of the RAPD-PCR and SDS PAGE were carried-out in order to detect the heterogenicity within the bacterial isolates. The results showed that there was a heterogenicity within the S.epidermidis isolated from naturally infected O.niloticus and C.carpio.
Results illustrated that, the mortality percent was 10% in O.niloticus when use B.subtilis as a Prophylactic treatment either in water or in diet. The mortality percent was 40%, 90% and 20% in subgroups treated with B.subtilis in water, diet and when use Erythromycin as a bath treatment respectively.
The mortality percent of C.carpio was lower than that of O.niloticus. The mortality rate was 6.7% and zero % when applied B.subtilis as a prophylactic measure in water and diet respectively. Using B.subtilis as a therapeutic agent showed a mortality percent of 10%, 53.3% in subgroups treated with B.subtilis in water and diet respectively. While the mortality rate reached 16.7% when used Erythromycin as a bath treatment.
Clinically, the infected O.niloticus with S.epidermidis showed severe unilateral and bilateral exophthalmia. The lesion was severe in the tail region beginning as detachment of scales at the peduncle region with emaciation beside stiffness of the caudal part of the body. In contrary, the infection was less severe in C.carpio than that of O.niloticus. The lesions were summarized in fin rot and erythema in addition to inflammation of swim bladder.
The use of B.subtilis as a prophylactic measure reduced the severity of the infection, especially when used as a prophylactic agent either in O.niloticus or C.carpio. Slight erythema on caudal fin and shallow ulcer at dorsal muscle. B.subtilis in diet also reduced the development of the disease and limit the signs to erythema with fin rot in O.niloticus. Experimentally infected C.carpio showed ulcer at the body wall 48 hrs post inoculation and the healing occur 1 week post infection.
Therapeutic effect of B.subtilis did not significantly affect the development of the disease in O.niloticus. In contrast to C.carpio the fish tried to withstand the infection.
The results proved that, there was no significant difference in final body weight of experimented O.niloticus groups when compared with control group which fed on basal diet without B.subtilis and there were highly significant increase in body gain percent and specific growth rate of subgroup7 than other groups. In addition, withdrawing Biogen® after infection with S.epidermidis from diet (Subgroup 2) showed a significant