Enteric red mouth disease

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Disease signs at the tank and pond level

• separation from other fish
• occasional nervous signs

Clinical signs of disease in an infected animal

• dark colour
• haemorrhages at base of paired fins and vent
• reddening of corners of mouth, gums, palate and tongue (hence the name of the disease)
• reddening of gill cover
• haemorrhaging in eyes

Gross signs of disease in an infected animal

• ascites (swollen abdomen from accumulated fluid)

Disease agent

The causative agent of enteric red mouth disease is the bacterium Yersinia ruckeri. The several serotypes of the bacterium vary in the severity of disease they cause. Yersinia ruckeri serotype 01a, the 'Hagerman strain', is exotic to Australia. Rainbow trout are particularly susceptible to this serotype, while Atlantic salmon are relatively resistant.

Host range

It should be assumed that all species in the host range are naturally susceptible.

Fish known to be susceptible to enteric red mouth disease:

Other species susceptible to infection:

Salmonids

• Arctic char (Salvelinus alpinus)
• brook trout (Salvelinus fontinalis)
• chinook salmon (Oncorhynchus tschawytscha)
• coho salmon (Oncorhynchus kisutch)
• cutthroat trout (Salmo clarkii)
• sockeye salmon (Oncorhynchus nerka)

Nonsalmonids

• bighead carp (Aristichthys nobilis)
• burbot (Lota lota)
• channel catfish (Ictalurus punctatus)
• cisco (Coregonus artedii)
• eel (Anguilla anguilla)
• emerald shiner (Notemigonus atherinoides)
• minnow (Pimephales promelas)
• silver carp (Hypophthalmichthys molitrix)
• sole (Solea solea)
• sturgeon (Acipenser baeri)
• turbot (Scophthalmus maximus)
• whitefish (Coregonus peled, C. muksun)

Presence in Australia

EXOTIC—not present in Australia.

However, a virulent form of Y. ruckeri (serotype 01b) causing a septicaemic condition in Atlantic salmon known as yersiniosis, is endemic to Australia. A characteristic of this form of the disease is the occurrence of pop eye (exophthalmus) and the formation of pronounced haemorrhages in the eye that give rise to the description of 'blood spot' disease. The prominent reddening of the corners of the mouth, gums and palate typical of enteric red mouth disease does not occur in yersiniosis.

Epidemiology

• Many other aquatic species are potential carriers but show no signs (e.g. some crustaceans, including freshwater crayfish).
• This disease is a septicaemia (bacteria infect the entire body through the blood).

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

Similar diseases

Viral haemorrhagic septicaemia, infectious haematopoietic necrosis, spring viraemia of carp, infectious salmon anaemia

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your state or territory hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your state or territory emergency disease hotline number, see Whom to contact if you suspect a disease.