Abstract
Isolation and identification of S. agalactiae from cultured sea bream by different microbiological methods, mortality rate, clinical signs, and postmortem lesions in sea bream in naturally and experimentally inoculated with a field sample of S. agalactiae. The aquarium trial was carried out with sea bream (Sparus auratus) in private fish farm at Borg El-Arab, Alexandria governorate Egypt. At total 50 of sea bream (Sparus auratus) was used during the study. The study lasted 10 weeks, starting with 50 ± 5 gram /fish. Prior to the start of the trial, the fish were fed with a commercial diet (45 percent CP, crude protein). Water quality parameters were monitored during fish acclimatization and throughout the trial. Water temperature, pH and dissolved oxygen remained within acceptable ranges for marine production during the trial. Our results concluded that, Streptococcus spp. (specifically S. agalactiae) is very pathogenic as they can affect sea bream which become a perfect host for Streptococcus infection. In addition, water quality parameter plays an important role in sea bream farming. In more specific, an optimum water quality parameter should be maintained to prevent “stress’’ in fish that can lead to outbreaks of disease. It can be concluded that the medicinal plant can help in prevention and control of bacterial infection in cultured fish, and because of their high resistance, to most antibiotics utilization in the prophylaxis or treatment of S. agalactiae infection should be avoided. The farmers must be used such approach to applied in the protocol of prevention of such infection in stead of chemotherapy.

Key words: Streptococcosis - sea bream Sparus auratus - Medicinal plant