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STREPTOCOCCUS INFECTIONS AMONG FARMED AND WILD TILAPIA FISH IN EGYPT

El-Sayed N. Abou El-Gheit.




Abstract

Streptococcal infections spread at the beginning of the summer among tilapia fish either farmed in brackish water farms at El-Faiyum Governorate, or cultured in floating cages in Damietta Branch of the Nile or wild tilapia collected from Rosetta Branch of the Nile. Streptococcal isolates from these three areas were beta and gamma hemolytic, gram positive cocci, negative to oxidase and catalase. They were identified by biochemical tests and API 20 STREP system as Streptococcus sanguis, Streptococcus milleri III, Streptococcus pyogenes and Enterococcus faecalis. These isolates infected 46, 60, 16 and 5 % of the total fish collected from the study areas respectively. The infected fish showed septiceamic clinical signs, exophthamia and sometimes with corneal opacity. Streptococcus infections caused 20 % mortalities among tilapia cultured in farms and 25 % among tilapia from the floating cages. Experimental inoculation of Nile tilapia, Oreachromis niloticus with streptococcal isolates exhibited clinical signs similar to those of the natural infection 2 days post-infection and caused 100 % mortalities within 7 days post inoculation with 1 X 107 c.f.u. fish-1 indicating the virulence of the isolates. All streptococcal isolates were highly sensitive to ciprofloxacin but resistant to penicillin. Ciprofloxacin and oxytetracycline remarkably decreased and stopped the mortality after the fourth to fifth days of the treatment of tilapia either cultured in farms or in floating cages.

Key words: Tilapia fish, Streptococcal infections, Streptococcus sanguis I, Streptococcus milleri III, Streptococcus pyogenes and Enterococcus faecalis, Ciprofloxacin and oxytetracyclin.






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