A survey on some risk factors and evaluation of their impacts on streptococcosis in rainbow trout farms in east of Mazandaran province (Haraz River)

One of the most important bacterial fish diseases which has caused some outbreaks in rainbow trout farms in Iran is streptococcusis .The farmers were suffering from huge economic losses due to the disease outbreaks in different rainbow trout farms in Iran. The aim of our study was to determine rate of streptococcusis incidence in different stage of growth in farmed rainbow trout in Haraze River, Mazandaran province. Fish and water samples were randomly collected and measured of randomly in10 selected farms, monthly throughout a year. After clinical observations, Isolation and recognition of strep strains were made using biochemical tests. Some Environmental factors include Nitrate, Nitrite, Temperature, pH, Ammonia and DO measured during sampling periods. According to our results 4.6% of juvenile samples showed clinical singe of streptococcusis while only0.7% of them had strep. Contamination .These rates in adult samples were 8.9 and 1 percent respectively. Major isolated bacterial strain was Streptococcus uberis. Incidence of streptococcusis in rainbow trout 20% affected by fluctuation of Nitrite, temperature and DO. Management of these factors can decrease rate of disease outbreaks