Nurse shark gill mycosis
Gill fungus is an infection caused by microscopic fungi that settle on the gills of the nurse shark. The gills are the organ that allows the animal to breathe underwater. This disease mainly affects nurse sharks kept in aquariums or tanks,...
What is it?
Gill fungus is an infection caused by microscopic fungi that settle on the gills of the nurse shark. The gills are the organ that allows the animal to breathe underwater. This disease mainly affects nurse sharks kept in aquariums or tanks, particularly when water quality is degraded. It remains rare but can be serious if not treated quickly.
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 shark breathes abnormally: gill movements faster or more difficult than usual.
We often observe a less active animal, which remains at the bottom of the pool longer than normal.
The appetite decreases, sometimes to the point of total refusal of food.
Swimming may become hesitant or unbalanced.
In advanced cases, the gill tissues may appear discolored, damaged or covered with an unusual deposit visible upon close examination.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Opportunistic fungi, belonging to groups naturally present in sea water, take advantage of a weakening of the fish or poor water quality to invade the gill tissue. These fungi are normally harmless but become pathogenic when conditions are favorable for them.
Poorly filtered or insufficiently renewed pond water promotes fungal proliferation.
Significant stress, for example during transport, capture or difficult cohabitation with other animals, weakens the shark's natural defenses.
Pre-existing injuries to the gills, caused by trauma or a parasite, open the door to infection.
Unsuitable water temperature or sudden variations in physicochemical parameters (salinity, dissolved oxygen) are also contributing factors.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian specializing in aquatic animals examines the animal, observes its swimming behavior and its breathing. A sample from the gills can be taken to be analyzed under a microscope or cultured to identify the fungus in question. The analysis of the water in the pond is also part of the assessment, because it often allows us to understand the origin of the problem.
Treatment
Treatment is based on antifungal treatments adapted to the aquatic environment, associated with an immediate improvement in water quality. General support for the animal, particularly to limit stress and promote healing, completes the care. Any intervention must be decided and monitored by a veterinarian specializing in aquatic fauna, because treatments in a marine environment require special precautions.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Maintaining impeccable water quality is the best protection: effective filtration, regular control of physico-chemical parameters and appropriate renewal of the water.
Limit sources of stress during handling, transport or changes in environment.
Monitor the general condition of the gills during routine checks carried out by keepers or the veterinarian.
Quarantine any new animal before its introduction into a shared pool.
Possible complications
If left untreated, the infection can gradually destroy the gill tissue, compromising the shark's respiratory capacity. Severe infection can lead to general weakening, increased susceptibility to other infections, or even death of the animal.
When to see a veterinarian
The shark breathes abnormally quickly or seems to have difficulty breathing.
The animal remains motionless at the bottom of the pool for longer than usual.
A refusal to eat food persists for several days.
Visible abnormalities appear at the level of the gills upon close observation.
Swimming becomes unusual or unbalanced.
Prognosis
The prognosis strongly depends on the speed of treatment. Detected early and associated with correction of breeding conditions, gill mycosis can be controlled. On the other hand, extensive damage to the gills before treatment significantly reduces the chances of recovery.
Frequently asked questions
Is gill fungus contagious to other fish in the pond?
The responsible fungi are often already present in the water. The risk depends above all on the quality of the water and the state of health of other animals, more than on strict direct contagion.
Can you treat an affected nurse shark yourself?
No. The aquatic environment and sensitivity of this species require the intervention of a veterinarian specializing in aquatic animals to make a reliable diagnosis and choose an appropriate treatment.
Does this disease also affect sharks in the wild?
It is mainly documented in animals kept in captivity, where water quality and stress are more easily involved. In the natural environment, it remains little reported.
How do you know if the water in the pool is the cause?
A complete analysis of water parameters, carried out in parallel with the examination of the animal, often makes it possible to identify an anomaly to be corrected.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 30 October 2026
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