Fungal infection of cockle gills
Fungal gill disease is a fungal infection affecting the gills of the cockle (Cerastoderma edule), a bivalve shellfish that lives buried in the sand of intertidal zones. A microscopic fungus invades the gill tissue, the organ that allows the...
What is it?
Fungal gill disease is a fungal infection affecting the gills of the cockle (Cerastoderma edule), a bivalve shellfish that lives buried in the sand of intertidal zones. A microscopic fungus invades the gill tissue, the organ that allows the animal to breathe and feed by filtering water. This disease is monitored in shellfish farms and natural beds because it can weaken populations and cause mortality, particularly during unfavorable environmental 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:
Signs are difficult to observe directly because cockles live buried and hidden. When examining the animal, discolored patches or zones—sometimes brownish or greenish—may be seen on the gills. Affected gill tissue may appear locally destroyed or necrotic (dead). Affected animals often show general weakness, reduced filtering activity, and progressive weight loss. In advanced cases, gill damage compromises respiration and feeding, which can lead to the animal's death, especially if other stress factors are present (high temperature, low oxygen, high stocking density).
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 results from invasion of the gills by a filamentous fungus that develops in the shellfish's respiratory tissue. This fungus typically takes advantage of prior weakening of the animal or degraded environmental conditions to establish and multiply. The infection usually remains localized to the gills but may spread if the animal is severely weakened.
Several factors can promote the development of branchial fungal infection in cockles: poor water quality (pollution, excessive organic matter), high water temperature, low dissolved oxygen, high density of shellfish on the same site, stress from transport or handling, and general weakness in the animal due to other diseases or parasites. Farming areas with insufficient water turnover are particularly at risk.
Transmission
Transmission occurs through water via fungal spores present in the environment, which contaminate the gills of healthy shellfish through contact with sick animals or contaminated sediments.
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 the gills by a specialist in mollusc pathology, usually after opening the shell and viewing affected tissues under a microscope. Laboratory analysis can identify the fungus responsible and confirm the fungal nature of observed lesions, ruling out other possible causes of mortality.
Treatment
There is no curative treatment that can be applied to individual shellfish in natural or extensively farmed settings. Management relies mainly on environmental prevention measures and improvement of farming conditions to strengthen the natural resistance of the animals.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention mainly relies on good management of the farming environment: maintaining satisfactory water quality, avoiding overstocking of shellfish, ensuring proper water turnover, and limiting sources of organic pollution. Regular monitoring of beds and farm batches allows early detection of abnormal mortality. Reducing stress during handling and transport also helps protect animals from increased vulnerability.
Possible complications
Severe damage to the gills can result in respiratory and feeding failure in the cockle, leading to marked weakness and then death. In farming operations, the disease can contribute to episodes of mass mortality, particularly in combination with other environmental stress factors.
When to see a veterinarian
Observation of abnormal or unexplained mortality in a batch or bed of cockles.
Presence of unusually weak shellfish, with poor response to stimuli, or failing to close normally.
Discoloration or abnormal appearance visible in tissues when opening shellfish.
Suspicion of declining water quality in a farming area.
Prognosis
Prognosis depends on the extent of gill damage and environmental conditions. Mild gill involvement with rapid improvement in water quality may allow some recovery, but extensive gill damage typically carries a guarded prognosis, with risk of individual or mass mortality if stress conditions persist.
Frequently asked questions
Is gill rot fungal disease in shellfish dangerous for humans?
No, this disease affects shellfish only and is not transmissible to humans. It poses no risk for consumption, provided that standard sanitary rules are observed.
Can a shell affected by branchial fungus be treated?
There is no individual treatment for shellfish. Management consists of improving environmental conditions (water quality, stocking density, oxygenation) to limit disease spread and promote the resilience of remaining animals.
How can I tell if my shells are affected?
The signs are only visible after opening the shell, by observing the appearance of the gills. Abnormal mortality in a batch should raise concern and prompt examination of samples by a specialist.
Can this disease affect other shellfish?
Gill mycoses similar to those observed can affect other filter-feeding bivalves living under comparable conditions, although each species may display different sensitivities.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 30 August 2026
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