Incidence of streptococcusis in rainbow trout (Onchorhynchus mykiss ) farms in Haraz River in Mazandaran Province, Iran

One of the most important bacterial fish diseases which have caused some outbreaks in rainbow trout farms in Iran is streptococcusis .The farmers have been suffering from huge economical losses due to the disease outbreak in different rainbow trout farms in Iran. The aim of present study was to determine the rate of streptococcusis incidence in different growth stage in the farmed rainbow trout in Haraz River in Mazandaran Province, Iran. Fish specimens along with water samples were collected from 10 haphazardly selected fish farms on a monthly basis throughout a year. After clinical observations, isolation and recognition of strep strains were undertaken using biochemical and PCR tests. The results showed that 4.6% of juvenile fish showed clinical sings of streptococcusis while only 0.7% had strep. contamination. These rates in adult specimens were 8.9 and 1 percent, respectively. The main isolated bacterial strain was Streptococcus uberis .