Gill fungal infection in sturgeon
Gill fungal infection, also called branchiomycosis, is an infection of the sturgeon's gills caused by aquatic fungi. These fungi invade the blood vessels in the gills, blocking blood circulation. The sturgeon's respiratory system becomes se...
What is it?
Gill fungal infection, also called branchiomycosis, is an infection of the sturgeon's gills caused by aquatic fungi. These fungi invade the blood vessels in the gills, blocking blood circulation. The sturgeon's respiratory system becomes severely damaged. This disease mainly affects sturgeon kept in tanks or aquaculture settings, especially when water quality is poor. It can progress very rapidly and cause the death of many fish within days if left untreated.
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 sturgeon swim near the surface seeking oxygen. They breathe rapidly and appear labored even at rest. The gills develop a mottled appearance, with pale or grayish patches mixed with darker areas, due to tissue death from blood loss. The fish becomes lethargic, eats less, and may rub against the tank walls or decorations. In severe cases, fish can die quickly, sometimes with no other visible signs before death.
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 aquatic fungi that develop in water and infect gill tissue. These fungi penetrate the small blood vessels in the gills and multiply there, causing clots and interruption of local circulation. Tissues deprived of blood die, progressively destroying the sturgeon's ability to breathe normally.
Water rich in organic matter or contaminated water strongly favors the development of responsible fungi. High water temperature, high fish density in the tank, lack of dissolved oxygen, and chronic animal stress are aggravating factors. Poorly maintained tanks with stagnant or infrequently renewed water carry higher risk.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
A fish veterinarian examines the gills with the naked eye and then under a microscope to identify the characteristic fungal filaments in affected tissues. A gill tissue sample is often needed to confirm the diagnosis and rule out other causes of respiratory problems, such as bacterial infection or gill parasites. Water quality testing of the tank forms an integral part of the diagnostic approach.
Treatment
Treatment combines immediate improvement of water quality with the use of antifungal medications suitable for fish, applied to the tank water under veterinary supervision. Reducing stress and optimizing oxygenation are essential to support recovery. In some cases, isolating sick fish prevents spread throughout the tank.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention hinges above all on maintaining good water quality: efficient filtration, regular water changes, removal of organic waste, and consistent monitoring of oxygenation. Overcrowding of tanks should be avoided and stress factors for sturgeon minimized. Regular testing of water parameters (temperature, oxygen, ammonia) helps detect conditions that favor disease development early on. Quarantining new fish before introducing them into a tank is also recommended.
Possible complications
Without prompt intervention, destruction of gill tissue can become irreversible, leading to severe respiratory failure. The disease can spread rapidly throughout the tank, causing significant losses among cultured sturgeon. Secondary bacterial infection may also complicate the course of the disease.
When to see a veterinarian
One or more sturgeon swim abnormally near the surface or appear to be gasping for breath.
The gills look pale, marbled, or discolored on examination.
Appetite loss or lethargy affects multiple fish in the same tank.
Unexplained deaths occur in the tank, even if isolated.
Prognosis
The prognosis depends on how quickly treatment is started. If the disease is caught early and water quality is corrected promptly, many fish can survive. However, if the infection is advanced or affects a large portion of the tank population, losses may be substantial despite treatment.
Frequently asked questions
Can gill mycosis affect fish other than sturgeon?
Yes, this disease affects many species of farmed and ornamental fish, not just sturgeon. It appears under similar water conditions regardless of the species.
Is this disease dangerous for humans?
No, gill fungus in fish is not transmissible to humans. It only affects fish living in water that is conducive to the development of the fungi responsible for it.
Can a sturgeon be saved if its gills are already severely damaged?
This depends on the extent of the damage. If a large portion of the gill tissue is destroyed, the chances of recovery are poor even with treatment, since the respiratory organ can no longer function properly.
How can I tell if my pond water is promoting this disease?
An excess of organic matter, stagnant water, elevated temperature, or lack of oxygen are warning signs. Having the water regularly analyzed helps prevent this risk.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 23 August 2026
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