Enteric red mouth disease (also known as Yersiniosis) is one of the most significant bacterial infections in coldwater fish farms that cause significant mortalities and economical losses in the salmonids fish farms, especially in rainbow trout (Oncorhynchus mykiss). ERM is caused by the gram negative pathogen bacteria Yersinia ruckeri that has five O-serotypes (O1, O2, O5, O6 and O7), five outer membrane protein types (OMP types 1–5) and two biotypes 1 and 2. The disease has a wide geographical distribution in various fresh or sea water fish. More than twenty species mainly of Salmonide origin have been affected and this number is likely to rise in the future following the introduction of new species and the increase of aquaculture trade. The disease can affect fish of all age classes but is most acute in small fish up to fingerling size. Affected fish may reveal different clinical symptoms depending on species, age and temperature. The most characteristic and common clinical signs of the disease include lethargic behavior and inactivity, swimming near the surface, anorexia, and darkening of the skin. The reddening of the throat and mouth, caused by subcutaneous haemorrhaging and exophthalmos are commonly present. Different diagnostic methods have been used for Y. ruckeri, including culturing, serological, biochemical tests, histopathological studies and molecular techniques. This review summarizes the past, present and future state of yersiniosis with emphasis on status of this disese in Iran. Also, some criteria in diagnosis, control and prevention of ERM were discussed.