الفهرس 
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Abstract
Diseases problems in cultured sea bass Dicentrachus Labrax reared in cages from Fingerlings until marketing size in Mariout Valley, King Mariout, Alexandria Province
This study was carried-out for, evaluation of the water quality of the farms included naturally infected sea bass during the different season, assessment of the heavy metals in water of the farms included naturally infected sea bass during the different season, determine and identify the common bacterial infection in different stages of cultured sea bass during the different season, experimentally infected the sea bass with the Vibrio alginolyticus and Vibrio parahemolyticus, investigate the antimicrobial sensitivity of the vibrosis spp.
The aquarium trial was carried out with European seabass (Dicentrarchus labrax) in private fish farm at Borg El-Arab, Alexandria governorate Egypt. At total 50 of seabass 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.
For diagnosis of different diseases affecting European seabass (Dicentrachus labrax) we depend upon the Gross clinical examination, Postmortem (PM) examination, Parasitological and Mycological examinations, Mycological examination, Physico-chemical analysis of water samples, Bacteriological examination, biochemical and Histopathological examination.
Our results indicated that :
1. European seabass (Dicentrarchus labrax) is the most important commercial marine fish widely distributed in Mediterranean countries. Egypt produces 14% of cultured D. labrax and Sparus aurata in the Mediterranean region, and it is considered the third major producer after Turkey and Greece.
2. Climate change represents the most dangerous environmental challenges for fish farming, global warming is recognized as the most significant environmental problem affecting the earth in the last decade. It has been implicated in mass mortalities of several aquatic species, including plants, fish, corals and mammals.
The current study revealed that the water quality of cultured sea bass was highly significant affected in relation to the season except the PH of water was non-significant changes all over the year. The dissolved oxygen was severally decreased during the summer and autumn season while, it was the highest in the winter. On the other hands, the highest mean of salinity, NO2, NO3, ammonia and temperature were 3.8, 15.8, 0.094, 8.3, 0.84 and 32.6, respectively in the summer seasons. This results that may be due to the solubility of oxygen is reversely proportional to water temperature, so dissolved oxygen significantly decreased with increased water temperature. Water temperature fundamentally impacts fish physiology and biochemistry by activating many enzymatic systems at higher water temperatures.
The increase of ammonia in all studied seabass farms this indicating exposure of fish to chronic ammonia toxicity and decreasing the dissolved oxygen enhanced ammonia toxicity. chronic ammonia toxicity directly affects the survival rate, inducing skin, fin and tail erosions.
There is highly significant different between the different heavy metal concentrations and the different seasons. The copper, cadmium, lead and iron were the highest above the permissible limit in the summer seasons, that were 0.783, 0.0251, 0.124 and 2.523, respectively. In contrast, the lowest percentage of copper (0.130) and iron (0.522) with non-detection of cadmium and lead were in the winter seasons. The heavy metal concentrations were within the permissible limit in the winter and spring seasons.
Vibrio and Aeromonas species are amongst the most commonly reported fish bacterial pathogens, usually in association with poor water quality or after handling.
The clinical examination of fish showed that the fish behave clinical signs of sever corneal hemorrhagic opacity, darkness area over the dorsal region and hemorrhages at the caudal peduncle area and hemorrhagic over the dorsal musculature and pectoral fins.
The post mortem examination of naturally infected fish showed that, the liver had mottled appearance with the presence of numerous necrotic foci. Kidneys were congested and enlarged with distended abdomen was found in few cases of naturally infected fish.
The prevalence of natural bacterial infection in cultured sea bass was the highest in the adult fish (72%). Moreover, the prevalence of bacterial infection in fingerling sea bass fish was (75%) the highest in the summer season followed by autumn (70%), while was the lowest in the winter season (20%) followed in the spring (30%). On the hand, the prevalence of bacterial infection in adult sea bass was the highest in the summer (90%), in contrast was the lowest (40%) in the winter season.