الفهرس 
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Abstract
In the present investigation, a total of 150 cultivated white leg shrimp (Litopenaeus vannamei) of different body weights and lengths were collected randomly and seasonally for viral and bacterial identification. They were examined freshly from the Suez governorate from (March 2020 to November 2020). The signs and the lesions of septicemia were revealed on some shrimps. Isolation and identification of bacteria are on TCBS, Aeromonas isolation medium, Pseudomonas isolation agar and XLD media. The traditional diagnostic method showed that isolated bacteria were Vibrio aginolyticus, Vibrio parahemolyticus, Vibrio campbellii, Vibrio fluvialis, Aeromonas hydrophila, Pseudomonas florescence and Proteus vulgaris. Isolated bacteria showed different chemical reactions confirmed by API 20 systems. PCR yielded a single amplification pattern of 450-bp & 338-bp & 120-bp and130-bp size products were characteristic for V. parahemolyticus, V. alginolyticus, V. campbellii and Aeromonas hydrophila respectively.
Concerning White Spot Syndrome Virus (WSSV) identification, PCR and sequencing for WSSV, they give byproduct of 232-bp size products and it confirmed that it was characteristic for white spot syndrome virus by 100% similarity. The prevalence of V. Parahemolyticus and V. cambpellii was the highest in the summer season (58 %) & (44 %) followed by the autumn season (42%) & (40 %) then the spring season (26%) & (18%) respectively. While V. alginolyticus & V. fluvialis prevalences were (34 %) & (20 %) in spring season followed by autumn season (54 %) & (26 %) then summer season (62%) & (34%). The prevalence of Aeromonas hydrophila was (26 %) in the spring season followed by the summer season (40 %) then the autumn season (44%).The prevalence of Pseudomonas flurescence was (14 %) in the spring season followed by the autumn season (18%) then the summer season (20%). Finally, Proteus vulgaris prevalence was the highest in the summer season (16%) then followed by the autumn season (10%) and finally spring season (8%). The highest seasonal prevalence of White spot syndrome virus among infected shrimp was recorded in the autumn season (60 %) followed by the summer season (6 %) and spring was the lowest season (0%). The histopathological alterations of infected L. vannamei shrimp showed cellular degeneration globules with connective tissue detachment, sloughing, broken muscle fibers with haemocytic infiltration, accumulation of inclusion bodies, atrophy of the haemolymphatic lacuna of branchial lamellae and cell proliferation. Concerning to water quality; Salinity, temperature and pH during the study period were significantly higher in the summer season compared to the other seasons.