Shark gill mycosis
Gill mycosis is a fungal infection (caused by a fungus) that affects the gills, the respiratory organ of sharks and fish in general. \n\nIn the tiger shark, this disease remains rare in the wild but can occur in captivity, particularly in p...
What is it?
Gill mycosis is a fungal infection (caused by a fungus) that affects the gills, the respiratory organ of sharks and fish in general. \n\nIn the tiger shark, this disease remains rare in the wild but can occur in captivity, particularly in public aquariums or during transport, when water conditions deteriorate. \n\nThe fungus settles on the already weakened gill tissues, which disrupts the gas exchanges essential to the animal's breathing.
Key point
This disease can be life-threatening for the animal if it affects a significant portion of the gill tissue, due to the essential role of the gills in respiration.
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 animal shows abnormally rapid or labored breathing, visible by more marked movements at the level of the gill slits. \n\nWe can observe slowed down, hesitant, or on the contrary agitated swimming, as well as rubbing behavior against the walls or bottom of the pool, a sign of discomfort in the gills. \n\nA loss of appetite and general fatigue often accompany the infection, especially if it progresses without treatment. \n\nIn advanced cases, the gill tissues may show areas of discoloration, necrosis (dead), or covered with an unusual deposit, visible only upon close examination by a specialist.
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 opportunistic fungi, i.e. microorganisms that occur naturally in the aquatic environment but only become problematic when the animal's defenses or water quality are weakened. \n\nCertain families of aquatic fungi, particularly genera close to Saprolegnia or Aspergillus, are usually involved in this type of damage in cartilaginous fish.
Poor quality water, with insufficient oxygen levels or chemical pollutants, greatly encourages the appearance of this mycosis. \n\nThe stress linked to transport, capture or a sudden change in environment weakens the shark's immune system and makes it more vulnerable. \n\nPre-existing injuries to the gills, caused by shock, a parasite or bacteria, create an entry point for the fungus. \n\nOverpopulation in a tank or captive space also increases the risk, as does water temperature unsuitable for the species.
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 a thorough visual examination of the gills by a veterinarian specializing in aquatic or exotic animals, often carried out under light sedation for the safety of the animal and the caregiver. \n\nSamples of gill tissue can be analyzed in the laboratory to precisely identify the fungus in question and rule out other possible causes such as bacterial or parasitic infection. \n\nAnalysis of the water quality of the basin is an integral part of the diagnostic process, because it directs towards the triggering factors.
Treatment
Treatment is based on immediate improvement in water quality, considered an essential prerequisite for any cure. \n\nAntifungal treatments adapted to the aquatic environment can be used under strict specialized veterinary supervision. \n\nIn some cases, medicated baths or water salinity adjustments are considered as additional measures, always under professional supervision.
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 most important preventive measure: effective filtration, regular monitoring of oxygenation and physicochemical parameters. \n\nLimiting stress during handling, transport or pool changes considerably reduces the risk of immune weakening. \n\nRegular veterinary monitoring of animals in captivity allows for early detection of any injury or gill abnormality before an infection sets in. \n\nAvoiding overpopulation and respecting the temperature parameters specific to the species also help to limit stress factors.
Possible complications
Without treatment, the infection can spread to the entire gill tissue, seriously compromising the animal's respiratory capacity. \n\nSevere respiratory distress can set in, leading to generalized weakening or even death of the animal in the most serious cases. \n\nDamaged gill tissues can also become the entry point for secondary bacterial infections, worsening the clinical picture.
When to see a veterinarian
The animal exhibits abnormally rapid or labored breathing.
A repeated friction behavior against the walls of the pool is observed.
Loss of appetite or unusual lethargy persists.
Discolored or abnormal areas are visible on the gills upon close observation.
The water quality of the basin has recently deteriorated or a stressful event has occurred (transport, handling).
Prognosis
The prognosis strongly depends on the speed of treatment and the severity of the damage at the time of diagnosis. \n\nDetected early and associated with improved environmental conditions, the infection can be brought under control with a good recovery. \n\nOn the other hand, extensive damage or late treatment significantly lowers the chances of recovery, due to the vital role of the gills in respiration.
Frequently asked questions
Is the tiger shark in the wild at risk of this disease?
The risk is much lower in a natural environment, where the quality of the water and the absence of stress limit opportunistic infections. This mycosis is mainly documented in captive or weakened animals.
Can this mycosis be transmitted to other fish in the same pond?
The responsible fungi can be present in the water and affect other fish that are already weakened, especially if environmental conditions remain degraded. Monitoring of the entire basin is recommended.
Can this disease be prevented without veterinary intervention?
Maintaining water quality and reducing stress are essential, but any clinical signs must be evaluated by a veterinarian specializing in aquatic animals, who is the only one authorized to confirm the diagnosis.
Is this disease common in tiger sharks?
It remains relatively rare, with most documented cases involving animals in captivity or subjected to significant stressful conditions.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 24 September 2026
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