Fungal Gill Disease in Clams
Fungal gill disease in clams is a condition caused by a microscopic fungus that attacks the gills—the organ that allows clams to breathe and filter water. This infection mainly affects shellfish farming operations in coastal areas, particul...
What is it?
Fungal gill disease in clams is a condition caused by a microscopic fungus that attacks the gills—the organ that allows clams to breathe and filter water. This infection mainly affects shellfish farming operations in coastal areas, particularly in lagoons. It can lead to significant mortality if not detected early, especially in young clams weakened by environmental stress.
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 clams show general weakness and reduced activity, visible as incomplete or abnormal shell closure. Body thinning inside the shell is sometimes observed, indicating poor nutritional condition resulting from difficulty filtering water properly. The gills, when examined by a specialist, show characteristic changes: discoloration, localized swelling, or filamentous lesions. These signs are not visible to the naked eye for an untrained farmer, which is why regular herd monitoring is important.
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 filamentous fungus capable of colonizing gill tissue in bivalve mollusks. It develops preferentially in degraded water conditions with high organic load or fluctuating salinity. The fungus takes advantage of weakened natural defenses in the clam to establish and spread in respiratory tissues.
Overcrowded rearing conditions facilitate disease transmission between clams. Poor water quality rich in organic matter or contaminated water weakens the clams' natural defenses. Sudden changes in temperature or salinity, as well as stress from transport or handling, increase susceptibility to this fungal infection. Young clams and individuals already weakened by another disease are at higher risk.
Transmission
Transmission occurs mainly through contaminated water, which carries fungal spores from one individual to another within the same basin or production zone.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis is based on examination of gill tissue, generally performed in a specialized laboratory using samples taken from diseased or recently dead animals. Microscopic observation allows characteristic fungal filaments to be identified. Additional testing may be necessary to confirm the species of fungus involved and rule out other bivalve diseases.
Treatment
There is no individual curative treatment applicable in farm settings for this fungal disease of bivalves. Management relies essentially on disinfection measures within the rearing environment and removal of sick or dead animals to limit spread. In certain cases, antifungal products suited to aquaculture may be considered under specialist guidance, but their use remains limited and regulated.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention focuses above all on maintaining good water quality in rearing tanks or production areas: avoid overcrowding, control organic load, and monitor physical and chemical parameters. It is recommended to quarantine new batches before introducing them into a healthy farm. Regular health monitoring of the stock, with routine checks, allows early detection in cases of unusual mortality.
Possible complications
Without corrective measures, the disease can cause significant mortality within a batch or tank, with considerable economic consequences for producers. Weakened clams also become more vulnerable to secondary opportunistic infections.
When to see a veterinarian
Unusual or unexplained mortality observed in a batch of clams.
Clams that no longer close their shells properly.
Visible weight loss or abnormal opening behavior in the stock.
Suspected decline in water quality associated with signs of disease.
Prognosis
The prognosis depends on how quickly the disease is detected and sanitation measures are put in place. Early intervention on water quality and removal of affected animals can limit the spread of the disease. Conversely, late detection exposes the affected farm to significant economic losses.
Frequently asked questions
Is gill mycosis in clams transmissible to humans?
No, this disease is specific to bivalve mollusks such as clams and presents no known risk to humans.
Can an individually affected clam be treated?
No, there is no practical individual treatment for farmed bivalves. Management is carried out at the batch or tank level, through environmental sanitation.
How do you know if your clams are diseased?
Only laboratory examination of gill tissue can confirm the disease. Abnormal mortality should raise concern and prompt consultation with a specialist in mollusk pathology.
Can this disease affect other shellfish?
Some closely related fungi can affect other bivalves, but each mollusk species has its own sensitivities; a species-specific diagnosis remains necessary.
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 30 August 2026
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