الفهرس 
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Abstract
6- Crabs are decapod crustaceans make up 20% of all marine crustaceans caught, farmed, and consumed worldwide. These are a source of high quality protein and omega -3 fatty acids and rich in sodium, potassium and phosphorus with good amounts of iron, zinc, copper and manganese. It has a good amount of vitamin A, C, B6, thiamine, riboflavin and is considered in some parts of the world as a delicacy for human. Blue crabs are a host to a suite of viruses, bacteria, fungus, protozoans, and parasites that can cause mortality or reduce marketability, And once infected became a source of infection to other crustaceans and fishes that live in the same places and some of these strains have zoonotic importance as they transmitted to human presenting a human health risk.
The present study was planned to investigate the bacteriological studies on crabs in Suez Canal.
A total of 250 shell diseased crabs were collected and taken alive from different localities of Suez Canal (port-said Governorate and El kantarah region, Ismailia Governorate) 125 from each Governorate. Samples were taken monthly in the summer season from June to August 2013 . These samples were transferred alive in tanks to the microbiological lab. in the Fish Diseases Department, Central Laboratory for Aquaculture Research in Abbassa, Sharkia and subjected to clinical, postmortem, bacteriological examinations. also a total number of 135 apparently healthy crabs, free from any shell lesions were collected and taken alive from the Suez Canal ( port-said Governorate )were used in the experimental infection (pathogenicity test. The present study revealed the following:1-Isolation of 914 isolates from crab organs (exocuticle, muscles, gills, haemolymph and hepatopancrease) and were identified according to the morphological and biochemical tests to four strains of bacteria belonged to Vibrio alginolyticus, Listonella anguillarum, Aeromonas Veronii and Pseudomonas anguilliseptica. The number of isolates for Vibrio alginolyticus was 448 isolates by incidence of 49.02%, Listonella anguillarum was 231 isolates by incidence of 25.27%, Aeromonas veronii was 108 isolates by incidence of 11.82%, and Pseudomonas anguilliseptica was 127 isolates by incidence of 13.89%. It was found that Vibrio alginolyticus, Listonella anguillarum, Aeromonas veronii and Pseudomonas anguilliseptica were highly isolated from the haemolymph by ratio of 94%, the muscles by ratio of 89.6%, then from exocuticle by ratio of 79.2%, followed by the gills by ratio of 75.6%.while it was less isolated from the hepatopancrease by ratio of 27.2%.<The common clinical signs observed on diseased crabs showed lethargy, weakness and slowly swimming with varied degree of shell lesions appeared as discoloured patches ( off-white and brownish black patches) on the dorsal and sometimes on the ventral surfaces of the crabs, that later spread over the appendages and progressed to soft, fragile and perforated shell. Moreover, the appendages showed foci and ulcers with variety of shapes and stages most frequently located on the first pair of legs (cheliped), and sometimes major appendage was lost. The eye stalks of some examined crabs were affected and became protruded and edematous (Exophthalmia) and discoloration in the eye iris. The pregnant female crabs (sponge crab), the sponge showed alteration in colour from normal yellow to abnormal blackish discolouration and has offensive odor.3-The common postmortem findings in diseased crabs revealed turbidity of the haemolymph and the heart area engorged with turbid haemolymph, the gill lamellae were adhered each other and changed their color to black and upon exploration of apron of diseased crabs showed brownish black discoloration of underlying organs (pleopods, intestine and genitalia.4-The pathogenicity test revealed that bacterial isolates recovered from naturally infected crabs were virulent to apparently healthy crabs showing nearly the same clinical signs and postmortem findings observed in naturally infected crabs. The mortality rate was 20–40 % in crabs by scarification route of experimental infection noticed along 4 weeks and 100% by injection route within 5hrs–3 days due to isolated bacteria.5-V. alginolyticus was sensitive to Norofloxacin and Ciprofloxacin and resistant to Amoxicillin and Ampicillin and intermediate to Amikacin and Trimethoprim-Sulfamethoxazole.6-L. anguillarum was sensitive to Norofloxacin and Ciprofloxacin and resistant to Amikacin, Amoxicillin, Ampicillin and Trimethoprim-Sulfamethoxazole. 7-A. veronii was sensitive to Norofloxacin and Ciprofloxacin and resistant to Amikacin, Amoxicillin, Ampicillin and Trimethoprim-Sulfamethoxazole.8-P. anguilliseptica was Sensitive to Norofloxacin and Ciprofloxacin and resistant to Amikacin , Amoxicillin , Ampicillin and Trimethoprim-Sulfamethoxazole.