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Diseases of finfish

Viral diseases—Epizootic haematopoietic necrosis

CLICK ON IMAGE TO ENLARGE epizootic haematopoietic necrosis

Mass mortality of redfin perch. Note the small size of individuals affected and swollen stomach of fish at the centre of the photograph

Source: anonymous

CLICK ON IMAGE TO ENLARGE epizootic haematopoietic necrosis

Note characteristic haemorrhagic gills of the redfin perch on the left

Source: anonymous

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 farm level
Disease signs at the tank or pond level
Clinical signs of disease in an infected animal
Gross signs of disease in an infected animal

Disease agent

Epizootic haematopoietic necrosis (EHN) in Australia is caused by epizootic haematopoietic necrosis virus (EHNV), a systemic iridovirus (ranavirus).

Related viruses are responsible for causing the same disease in sheatfish and catfish in Europe (European sheatfish virus and European catfish virus).

In this guide, only EHN due to EHNV is discussed.

Host range

Fish known to be susceptible to EHN:
rainbow trout* (Oncorhynchus mykiss)
redfin perch* (Perca fluviatilis)
Macquarie perch (Macquaria australasica)
mosquito fish (Gambusia affinis)
mountain galaxias (Galaxias olidus)
silver perch (Bidyanus bidyanus)

* naturally susceptible (other species have been shown to be experimentally susceptible)

Presence in Asia–Pacific

Map showing presence in Asia–Pacific

EHN has been officially reported from Australia.


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

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 national 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 national emergency disease hotline number, see Whom to contact if you suspect a disease.

Further reading


The currently accepted procedures for a conclusive diagnosis of EHN are summarised at

These hyperlinks were correct and functioning at the time of publication. epizootic haematopoietic necrosis epizootic haematopoietic necrosis

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