Viral haemorrhagic septicemia of mackerel
Viral hemorrhagic septicemia (VHS) is a serious viral disease that affects many species of marine and freshwater fish, including mackerel. It is caused by a virus belonging to the Rhabdoviridae family, capable of causing internal bleeding a...
What is it?
Viral hemorrhagic septicemia (VHS) is a serious viral disease that affects many species of marine and freshwater fish, including mackerel. It is caused by a virus belonging to the Rhabdoviridae family, capable of causing internal bleeding and significant mortality. This disease is closely monitored by veterinary health authorities as it seriously affects wild populations and aquaculture. In mackerel, however, the infection remains less documented than in salmonids or other farmed fish.
Key point
A notifiable disease in many countries due to its potential impact on wild and farmed fish populations.
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 often display abnormal behavior: disorganized swimming, difficulty staying in open water, or on the contrary swimming in a spiral. We frequently observe a general depression, a loss of liveliness and a slowing down of movements. Hemorrhages may appear in the eyes, gills, skin or internal organs, visible upon close examination. Some fish exhibit abnormal darkening or paleness of the skin. In severe cases, rapid and massive mortality can occur without very significant prior signs, which makes early detection difficult in a natural environment.
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 virus from the Rhabdoviridae family, close to that which causes VHS in trout and other fish. Several strains or genotypes of this virus exist, some being more associated with marine fish such as mackerel, herring or sprat. The virus multiplies in host cells and causes vascular lesions causing characteristic hemorrhages.
Stress linked to variations in water temperature, high population density or environmental pollution can promote the clinical expression of the disease. Cold waters, especially in winter and early spring, are often associated with higher viral activity. The presence of other asymptomatic carrier fish in the same area also constitutes a risk factor for spread.
Transmission
The virus is mainly transmitted horizontally, that is to say from fish to fish, via water contaminated by secretions, urine or tissues of infected fish. Direct contact between fish in the same school or the same area favors the spread. Transmission by vectors such as certain piscivorous birds or by contaminated fishing equipment cannot be excluded but remains secondary.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The definitive diagnosis is based on specialized laboratory analyses, in particular the detection of the virus by cell culture or by molecular biology techniques such as PCR, carried out from organ samples such as the kidneys or the spleen. Clinical observation and hemorrhagic lesions guide the veterinarian or fish pathology specialist, but only laboratory analysis confirms the diagnosis.
Treatment
There is no specific antiviral treatment validated for this disease in wild or farmed fish. Management is essentially based on support measures limiting stress and, in a breeding context, on the isolation of affected fish to limit the spread.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
There is no vaccine available for mackerel against this disease. Prevention is mainly based on epidemiological surveillance of wild populations and neighboring farms, as well as strict biosecurity measures in the case of associated aquaculture. Avoiding the introduction of fish from infected areas and limiting environmental stress on captive populations are useful measures where management is possible.
Possible complications
The disease can cause massive and rapid mortality among affected populations. In surviving fish, general weakening and increased susceptibility to other secondary infections may persist.
When to see a veterinarian
Observation of unusual or massive mortalities in a population of mackerel or surrounding fish.
Fish exhibiting abnormal, disoriented or spiral swimming.
Observation of visible hemorrhagic lesions on the skin, eyes or gills.
Suspected disease in an aquaculture context requiring notification to the competent health authorities.
Prognosis
The prognosis is variable and depends on the viral strain, water temperature and the general condition of the affected populations. In severe outbreaks, mortality can be high in a short time. However, certain populations may present asymptomatic carriers without significant mortality, which complicates the assessment of the real risk in the field.
Frequently asked questions
Can mackerel viral hemorrhagic septicemia infect humans?
No, this disease is specific to fish and is not considered transmissible to humans.
Can we treat a mackerel suffering from this disease?
There is no specific antiviral treatment. The treatment aims above all to limit stress and the spread in the populations concerned, particularly in breeding.
Is this disease common in mackerel in the Mediterranean?
It is mainly documented in other marine and farmed species such as trout or herring. Its presence in mackerel remains less studied and varies according to geographical areas.
Should you eat potentially affected fish?
If in doubt about the health status of a fish, it is preferable not to consume it and to report the observation to a professional or competent authority.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 18 August 2026
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