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Octopus gill mycosis
Octopus gill mycosis is an infection caused by filamentous fungi that settle on the gills, the respiratory organ of the common octopus (Octopus vulgaris). This disease mainly affects animals that are weakened, injured or kept in poor qualit...
What is it?
Octopus gill mycosis is an infection caused by filamentous fungi that settle on the gills, the respiratory organ of the common octopus (Octopus vulgaris). This disease mainly affects animals that are weakened, injured or kept in poor quality water, in farms or in aquariums. The affected gills gradually become damaged, which hampers gas exchange and can endanger the animal's life. It is an uncommon but feared pathology in aquaculture and aquariums because it progresses quickly in this fragile animal.
Key point
Illness that can rapidly progress to respiratory distress in an otherwise fragile animal; rapid support is essential.
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:
The affected octopus becomes less active and hides more than usual. He often refuses the food offered. Its swimming may become irregular, with abnormal movements of the fins or exiting the water, reflecting respiratory difficulty. There may sometimes be a change in skin color, excessive mucus around the gills, or whitish to grayish filaments visible upon close examination of the gills. In advanced cases, the animal remains motionless at the bottom of the tank and breathes laboriously.
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 filamentous fungi (often related to genera found in other marine invertebrates) which colonize the gill tissue. These fungi generally take advantage of a breach in the animal's natural defenses: injury, stress, or general weakening.
Poor quality water, loaded with organic matter or poorly oxygenated, promotes fungal development. Skin or gill injuries, stress linked to transport or captivity, too high a breeding density, sudden variations in temperature or salinity, and an immune system already weakened by another disease also increase the risk.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Le diagnostic repose sur l'observation clinique de l'animal et l'examen rapproché des branchies, si possible sans stress excessif. A professional specializing in marine invertebrate pathology can take a gill sample for observation under a microscope, allowing the presence of fungal filaments to be confirmed and other causes such as bacterial or parasitic infection to be ruled out.
Treatment
Treatment aims first to correct the water quality and reduce the animal's stress. Antifungal treatments suitable for marine invertebrates can be considered under specialist supervision, taking into account the high sensitivity of octopuses to many chemicals. General support (nutrition, oxygenation) often accompanies treatment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention is based above all on good management of water quality: effective filtration, regular monitoring of physico-chemical parameters, and appropriate water renewal. Overcrowding in ponds or aquariums should be avoided, octopuses should be handled gently to limit injuries, and any animal showing signs of weakness should be quickly isolated. Quarantine of new arrivals is also recommended in breeding.
Possible complications
Without intervention, gill damage can worsen to the point of causing severe respiratory failure. Secondary bacterial infections can also be added, complicating the course and prognosis.
When to see a veterinarian
The octopus remains motionless or unusually hidden.
The animal has refused to eat for several days.
Labored breathing or abnormal movements in the coat are observed.
Abnormal filaments or deposits are visible near the gills.
Skin color changes markedly for no apparent reason.
Prognosis
The prognosis depends on the speed of treatment. Detected early and associated with a correction of breeding conditions, the evolution can be favorable. At an advanced stage, with severe respiratory damage, the prognosis becomes guarded, this species being by nature fragile in the face of stress and infections.
Frequently asked questions
Can octopus gill mycosis be transmitted to humans?
No, this disease is specific to marine invertebrates and does not present a known risk to humans.
Can we treat an affected octopus at home, in a domestic aquarium?
It is strongly recommended to hire a professional with knowledge of marine invertebrates, as octopuses are very sensitive to many conventional chemical treatments used in aquariums.
How to avoid this disease in breeding or aquariums?
Maintaining very good water quality, avoiding overpopulation and limiting stress and injuries are the best means of prevention.
Is this disease common in common octopus?
It remains poorly documented and relatively rare, but it is monitored in aquaculture because it can significantly affect already weakened animals.
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 11 August 2026
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This information is provided for educational purposes only and is not a substitute for a veterinary consultation. If you have any concerns about your animal's health, consult a veterinarian.
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