Streptococcosis is one of the economically important diseases in the aquaculture industry particularly in rainbow trout aquaculture causing remarkable annual losses. Streptococcosis is known as a zoonotic disease causing morbidity and mortality in some consumers. In this study the status of farmed rainbow trout contamination with Streptococcus iniae and Lactococcus garvieae was assessed. For this reason, during summer months, 64 apparently diseased trout were sampled from fish markets of Tehran and Karaj. Gram staining was performed on grown colonies and then gram-positive cocci were further characterized using biochemical and PCR assays. The obtained results showed that 56.23% (36 samples) of the samples were infected with the both bacterial pathogens. The prevalence of S. iniae and L. garvieae were 32.8 % (21 samples) and 23.43% (15 samples), respectively. The highest and lowest prevalence rate of S. iniae was observed in the samples of Karaj (15.62%) and Kahrizak (0%) markets, respectively. In the case of L. garvieae, the highest and lowest rates were obtained in Karaj/Kahrizak (7.81%) and Meidan-Nabi (1.56%) markets, respectively. The results revealed that in some markets, the prevalence of streptococcosis and lactococcusis in cultured rainbow were relatively high. Therefore, it is necessary to conduct further trials.
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