Infectious pancreatic necrosis of salmon
Infectious pancreatic necrosis (IPN) is a serious viral disease which mainly affects young farmed salmon, particularly at the fry stage and during passage into seawater (smoltification). It is caused by a very resistant virus in the environ...
What is it?
Infectious pancreatic necrosis (IPN) is a serious viral disease which mainly affects young farmed salmon, particularly at the fry stage and during passage into seawater (smoltification). It is caused by a very resistant virus in the environment. This disease is present in many salmon-producing countries and represents a significant economic challenge for aquaculture.
Key point
Mandatory notifiable disease in several countries due to its major economic impact on salmon aquaculture.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Affected fish swim abnormally, sometimes spiraling or sideways. They may remain motionless at the bottom of the pool or, on the contrary, swim frantically near the surface before dying.
There is often darkening of the skin, a swollen abdomen (bloating), and sometimes mild bulging (protruding eyes).
The appetite decreases sharply and the fish become lethargic.
Mortality can occur suddenly, particularly among fry and young smolts, with peaks that can affect a significant portion of a cohort within a few days.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by a double-stranded RNA virus belonging to the family Birnaviridae, which specifically infects cells of the exocrine pancreas and other digestive tissues of salmonids.
Fry and young smolts being transferred to seawater are the most sensitive. Stress linked to handling, transport, high stocking density or variations in temperature and water quality favors the appearance of the disease. Some genetic lines of salmon are more susceptible than others. The presence of asymptomatic carriers on a farm also constitutes a major risk factor for spread.
Transmission
The virus is transmitted horizontally, from one fish to another, through water contaminated with feces, mucus or infected tissues. It can also be transmitted vertically, from mother to eggs, which explains its persistence in certain breeding lines. The virus is particularly resistant in the aquatic environment and can survive for a long time outside the host, which facilitates its spread between ponds or breeding sites.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The aquaculture veterinarian or specialist in fish pathology establishes the diagnosis based on clinical signs, the history of the breeding site and above all laboratory analyses: search for the virus using molecular biology techniques, viral isolation on cell cultures, or examination of lesions under a microscope on samples of pancreas and digestive tissues.
Treatment
There is no specific antiviral treatment effective against this disease. Treatment is based on support measures: improvement of breeding conditions, reduction of stress, optimization of water and feed quality, in order to limit mortality and promote the recovery of surviving fish. Veterinary support makes it possible to adapt the management of the site during the episode.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention is based on strict biosecurity measures: disinfection of eggs and facilities, health control of broodstock, quarantine of new batches and limitation of fish movements between sites.
Genetic selection of salmon lines more resistant to the virus is increasingly used by hatcheries.
Vaccination of fish may be offered in certain at-risk farms, in addition to other measures.
Good management of water quality and reduction of stress during handling also limit the appearance of clinical outbreaks.
Vaccination
Vaccines exist in certain producing countries to protect fish at risk, particularly during the transfer phase in seawater. Their use is part of an overall biosecurity strategy and must be discussed with an aquaculture veterinarian.
Possible complications
Surviving fish can remain chronic carriers of the virus throughout their lives, constituting a source of contamination for other farmed animals. Secondary bacterial infections can add to the initial viral attack, worsening the clinical picture and mortality.
When to see a veterinarian
Sudden or unusual mortality in fry or young smolts
Fish swimming abnormally, spiraling or sideways
Marked loss of appetite and generalized depression in a batch of fish
Swelling of the abdomen associated with darkening of the skin
Any episode of clustered mortality requiring notification to the competent health authorities
Prognosis
The prognosis strongly depends on the age of the affected fish and the breeding stage. Mortality can be very high in fry and young smolts, while older salmon often survive infection but may remain carriers. The overall health management of the site greatly influences the evolution of the disease.
Frequently asked questions
Is infectious pancreatic necrosis dangerous for humans?
No, this disease only affects fish, particularly salmonids. It is not transmissible to humans and presents no risk for the consumption of fish from supervised farms.
Can we cure a salmon suffering from this disease?
There is no curative antiviral treatment. Care involves improving breeding conditions to help the fish overcome the infection. Some survive but may remain carriers of the virus.
How can a farm protect itself from this disease?
Prevention is based on biosecurity (disinfection, quarantine, control of broodstock), the selection of genetically more resistant lines and, in certain cases, vaccination of fish at risk.
Which fish are the most vulnerable?
Fry and young salmon being transferred to seawater (smolts) are the most susceptible and have the highest mortality rates.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 25 September 2026
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