Studies on Bacterial Pathogens in Some Marine Fishes in EL-Mansoura, Egypt

A total of 200 marine fish of two different species (100 Tilapia zillii and100 Mugil capito) were randomly collected from different markets, during different seasons. Fish subjected to clinical, postmortem and bacteriological studies. The common clinical signs were darkness of the skin, hemorrhage in the fins base, eyes and different parts of the body, abdominal distention, congestion in gills and increasing in mucous secretion. The Post Mortem findings showed white serous fluid in the abdominal cavity and sometimes tinged with blood and pale or congested liver, kidney and spleen. The bacteriological examination, revealed that the prevalence of bacterial pathogens among naturally infected marine fishes were A. hydrophila (52; 39.39%), V. alginolyticus (38; 28.79%), Ps. fluorescens (24; 18.18%), V. cholerae (10; 7.58%) and Ps. aeruginosa (8; 6.06%). The highest prevalence of bacterial infection was during summer (33.33%) followed by spring (24.42%), then autumn (21.97%), while the least prevalence was in the winter season (20.46%). A. hydrophila was highly pathogenic to T. zillii causing 100% mortality followed by V. alginolyticus causing (90%) mortality, then Ps. fluorescens (80%), Ps. aeruginosa (60%) while V. cholerae was non-pathogenic. The results of antibiogram revealed that ciprofloxacin and nalidixic acid were effective against A. hydrophila, while ciprofloxacin and rifampicin were effective against Ps. fluorescens. Ciprofloxacin and amikacin were effective against Ps. aeruginosa. While V. alginolyticus was highly sensitive to ciprofloxacin. High prevalence of pathogenic and resistant bacterial strains among marine fishes in Egypt, requires strict control measures from the responsible authorities.