Streptococcal septicemia in rainbow trout farm in Sabzevar

Objective: Streptococcal disease in fish is one of the most important diseases that can cause high mortality. Fresh water and marine water fish are susceptible to Stereptococosis. There are several other closely related groups of bacteria that can cause similar disease, including Lactococcus, Enterococcus, and Vagococcus. Stereptococosis occurs in chronic and acute form and regularly susceptibility to the pathogen can increase with stress. Strep can spread in a group of fish through oral routes, including contaminated food, or through water. Pathogen can live in mud, water and contaminated food for long time and it can tolerate high temperature and pH. Method & Materials: In a rainbow trout farm in Sabzevar in Khorasan Province, 5 days after enterance of fish with 5-7 gr weight , the fish with 150-170 gr weight showed mortality, and after few days mortality occurred in the new fish. Some fish were transmitted to the laboratory on ice. For diagnosis, culture of blood, liver and kidney on Blood agar and MC conkey was carried out. After 24 hours in 270C temperature, small white and round colonies revealed. In gram staining, we observed gram + cocci chains. After biochemical test, it was diagnosed as Streptococcal infection. Results & Conclusion: Clinical signs were: darkening, hemorrhages in fins, exophtalmia and fish showed seclusion in bottom of ponds. In necropsy findings we observed: hemorrhages and yellow mucus in intestine, pale liver with hemorrhage spots, enlarged reddened spleen and ascite in ventral cavity. Before detecting pathogen species, considering to intestinal problem, we recommended to decrease food to 50%. In antibiogram test, the pathogen was susceptible to oxytetracycline and severely susceptible to choloramphenicol. For preventing the transmission of this infection, it is necessary to quarantine the new fish entering to farm. Stress often plays a significant role in outbreaks of infectious disease in fish populations. Some stressors that have been associated with Strep outbreaks include high water temperatures (e.g., during the summer), high stocking densities, harvesting or handling, and poor water quality, such as high ammonia or nitrite concentrations (management stressors) and it can cause high mortality.

کلیدواژه ها:

Stereptococosis ، rainbow trout ، Sabzevar