Infection of rainbow trout with Streptococcus spp. in Isfahan Province

Objective: Streptococcus spp. infections occur in a variety of species of freshwater and salt-water fishes. These diseases maybe either chronic or acute and usually are associated with some type of stress. Currently, streptococcusis is the most serious disease problem affecting fish. At present, streptococcosis, as a zoonose disease between human and domestic animals, has infected worthy of a considerable parts of fish farms in Iran. Infection is accompanied by non observance of hygienic principles and environmental stresses. Consequently, warm weather, high concentration, transportation, starvation, infected food and etc can cause the disease and mortality in fishes. Method & Materials: In this investigation 72 sick fish that showed sings of disease wre collected from 6 rainbow trout farms, located inside the water transport channel in Isfahan Province. Water temperature in the farms was 18 - 22°C, weight of infected fishes was 150- 200 gr and mortality rate was 25 %. The samples were transported to the laboratory lively at standard condition and cultured on blood and kf media and then placed in incubator in 20°C. After24- 48 hours the results of bacterial growth evaluated and antibiogram test accomplished. Antibiogram read after 24 hours. Results & Conclusion: Observable clinical signs of disease were: vertical swimming, insensibility, dark color, exophthalmie and cornea turbidity. The necropsy findings were: hemorragies in eyes, operculum, base of fins, surrounding of anal and heart. The other signs were abdominal swelling and skin ulcers, bloody fluids in abdominal cavity, spleen hypertrophy, pale liver and pericardiatis and nephritis. In bacterial culture using kidney, Streptococcus spp. isolated from media. The bacterial sensitiveness to the antibiotics was enrofloxacin (75-100%), erythromycin (0-75%), flumequine (0-100%), oxytetracycline (0-75%) and sulfamide (0-100%), regarding to the sampling of each farm. Strep infections in fish can cause high mortality rates (> 50%) over a period of 3 to 7 days. Streptococcus spp. can be identified by their hemolysis patterns on blood agar, colony morphology, biochemical reactions, and serology to detect antigens. This pathogen has been treated with various antibiotics including penicillin, amoxicillin, ampicillin, clindamycin, chloramphenicol and enrofloxacin. Some isolates may be drug resistant. However, prevention of disease is always preferable and more profitable than treatment of disease outbreaks. Preventive medicine programs should be designed to minimize stress; maintain the best water quality possible; and minimize exposure to infectious agents by following appropriate disinfection and sanitation protocols.