Diseases of wild and farmed Finfish

Yersinia ruckeri ERM

Yersinia ruckeri is the causative agent of the salmonid disease enteric redmouth (ERM) and causes significant economic losses particularly in the rainbow trout farming industry.  Clinical signs include haemorrhaging around the mouth, intestines and other organs.  Popeye is also a common sign of ERM.  Y. ruckeri, as with many other aquatic pathogens, is naturally associated with the aquatic environment and is thought to initially infect via adhesion to the gill surface (Tobback et al 2010). 

Some strains have been shown to adhere to/ form biofilms on solid structures such as those on fish farms (Coquet et al 2002) which could explain recurrent outbreaks.   Although the optimal growth temperature of Y. ruckeri is 28ºC, the optimal temperature for infectivity is thought to be around 18ºC.  Enteric redmouth can be controlled mainly through the use of antibiotics although resistance to some antimicrobial agents exists.

Diagnosis

• Bacteriological culture and biochemical testing
• Histopathology
• Molecular confirmation