Infectious Pancreatic Necrosis in Trout
Infectious pancreatic necrosis (IPN) is a serious viral disease affecting mainly young trout, particularly fry and fingerlings raised in aquaculture. It is caused by a virus that destroys pancreatic tissue, an organ essential for digestion....
What is it?
Infectious pancreatic necrosis (IPN) is a serious viral disease affecting mainly young trout, particularly fry and fingerlings raised in aquaculture. It is caused by a virus that destroys pancreatic tissue, an organ essential for digestion. This disease occurs in many countries where salmonids are farmed and can cause significant economic losses in fish farms.
Key point
This disease carries potentially very high mortality in fry and young trout and can rapidly wipe out an entire group in farm conditions.
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:
Infected fish display abnormal swimming: some swim in circles, others remain motionless at the bottom of the tank or swim head-down. General lethargy and loss of appetite are often observed. The belly may appear swollen due to fluid accumulation. Whitish or mucoid fecal trails trailing behind the fish are a fairly characteristic sign. In some cases, blood may be seen in the faeces or unusually dark skin colouration. Mortality can be very rapid and affect large numbers of fish within days, especially in fry.
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 birnavirus, a hardy virus capable of surviving for long periods in water, sediments and rearing materials. It primarily infects pancreatic cells and sometimes liver and kidney cells, causing their destruction (necrosis).
Fry and young trout from a few weeks to a few months of age are the most susceptible; adult trout typically develop mild forms or show no symptoms. Stress from sudden changes in water temperature, high stocking density in raceways, poor water quality, or transport increase the likelihood of disease and worsen its severity. Introduction of fish or eggs from uncontrolled farms poses a major risk.
Transmission
The virus is transmitted directly from fish to fish through contaminated water, by contact with infected or carrier fish, and indirectly through rearing equipment, staff hands or fish-eating birds. It can also be transmitted from mother to egg (vertical transmission), which explains the difficulty in eradicating the disease in some farms. Surviving fish may remain carriers of the virus for life without showing signs and can silently spread it.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian or aquaculture specialist establishes a tentative diagnosis based on clinical signs and mortality rate observed in the raceway. Confirmation requires laboratory analysis: virus isolation on cell cultures or detection of viral genetic material using molecular techniques, performed on tissue samples from kidney, spleen, and pancreas. Microscopic examination of tissues may reveal the characteristic pancreatic lesions.
Treatment
No specific antiviral treatment exists. Management is primarily supportive: improving rearing conditions, reducing stress, optimizing water quality and nutrition to help surviving fish recover. Antibiotics may be used only for secondary bacterial infections, on veterinary advice.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention relies primarily on strict biosecurity measures: egg disinfection upon introduction, health screening of broodstock, quarantine of new groups, and regular disinfection of equipment and raceways. It is recommended to source eggs and fry from certified suppliers free of the disease. Reducing stress in fish through good water quality, appropriate stocking density, and gentle handling lowers the risk of clinical disease. There is no widely used vaccine in trout farming for this disease.
Possible complications
Complications include massive mortality in fry, stunted growth in survivors, and increased susceptibility to other bacterial or parasitic infections. Fish that survive may become chronic carriers of the virus and serve as a lasting source of contamination for the farm.
When to see a veterinarian
Unusual and rapid mortality in young trout in a pond.
Fish swimming in circles, upside down, or lying motionless on the bottom.
Complete loss of appetite in a batch of fry.
Whitish fecal filaments trailing behind the fish.
Recent introduction of new fish or eggs followed by signs of disease.
Prognosis
The prognosis is guarded in fry and young trout, which can suffer very high mortality during an outbreak. Older trout generally survive without apparent long-term effects but may remain carriers of the virus. Once the disease is established in a farm, complete elimination is difficult because of asymptomatic carriers and the virus's resistance in the environment.
Frequently asked questions
Is infectious pancreatic necrosis dangerous for humans?
No, this disease is strictly viral and specific to salmonid fish such as trout. It poses no risk to human health, including through fish consumption.
Can one treat a trout affected by this disease?
There is no curative antiviral treatment. Care consists in improving farming conditions to reduce stress and promote recovery in surviving fish.
How can I prevent this disease from entering my livestock operation?
The best protection consists of sourcing certified disease-free eggs and fingerlings, regularly disinfecting equipment, and quarantining any new batch of fish before introducing it into the main farm.
Can a fish that has survived illness become sick again?
A surviving fish can remain a carrier of the virus for its entire life without necessarily falling ill again, but it can transmit the virus to other fish, particularly to younger and more vulnerable ones.
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 23 August 2026
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