Enteric redmouth disease (ERM) is an emerging problem in aquaculture all over the world. ERM is caused by the gram-negative bacterial pathogen , which can infect salmonids and several other fish taxa and cause clinical signs of hemorrhaging on the body surface and in the intestine. Fish suffering from ERM exhibit exophthalmos, darkening skin, subcutaneous hemorrhage of the mouth and throat, perianal swelling with yellow fluid, and other deleterious outcomes up to and including death. When ERM appears in an aquaculture facility, a large number of fish may be affected over a short period of time. Various antibiotics are available for the treatment of ERM and vaccines can also be used in the treatment and prevention of this disease. Several methods such as ultrastructural examination and LAMP have been developed for ERM detection. However, these assays are generally laborious and time-consuming, and are not sufficiently sensitive. To establish a rapid and quantitative method for the detection of , a pair of specific primers was designed and synthesized based on the virulent gene gene was used as a standard to construct a standard curve. SYBR Green I real-time quantitative PCR assay was established for the detection of by optimizing experimental conditions. The established qPCR method was also applied to the detection of in tissues of artificially-infected rainbow trout. Our results showed that the designed primers had good interspecific specificity. The quantitative linear equation was =0.9958). The detection limit of qPCR method was 57 copies/μL, which is approximately 100-fold greater than conventional PCR. This qPCR method can accurately detect in rainbow trout. These results suggest that our qPCR method has the advantages of specificity, sensitivity, rapidity, and quantification, and can be used for rapid diagnosis of early-stage disease and quantitative detection of .