Fungal gill infection in hake
Fungal gill infection is a fungal infection affecting the gills of hake, a marine fish caught commercially and sometimes kept in captivity for observation or experimental aquaculture. This respiratory condition is caused by opportunistic fu...
What is it?
Fungal gill infection is a fungal infection affecting the gills of hake, a marine fish caught commercially and sometimes kept in captivity for observation or experimental aquaculture. This respiratory condition is caused by opportunistic fungi that colonize gill tissue, particularly when the fish is weakened or stressed. It remains poorly documented in wild populations but may appear in captive conditions or at high stocking densities.
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:
An infected hake shows visible respiratory distress: it swims near the surface or seeks areas with better water circulation, and breathing rate increases.
The gills may appear discolored, with grayish or dead tissue (necrosis) visible on close inspection.
The fish becomes lethargic, remaining still or swimming erratically.
Loss of appetite and progressive weight loss develop if the infection persists.
Rubbing against tank walls or the bottom may be observed, indicating gill discomfort.
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 infection is caused by opportunistic filamentous fungi belonging to genera capable of growing in saltwater on already weakened tissues. These fungi take advantage of preexisting gill damage, significant stress, or decreased immune defenses in the fish to establish and multiply.
Poor water quality in tanks or cages promotes the disease. High stocking density increases stress and contact between fish, which facilitates spread. Pre-existing gill injuries from handling, trawling, or parasites create an entry point for fungal infection. Water rich in organic matter or with poor circulation favors fungal growth.
Transmission
Spread occurs mainly through water contaminated with fungal spores, particularly in confined environments with high fish densities.
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 clinical observation of the gills and the fish's behavior, supplemented by gill tissue sampling for microscopic examination. A fish pathology specialist can identify the fungal species through culture or laboratory analysis, which guides selection of the most suitable treatment.
Treatment
Management involves immediate improvement of water conditions (oxygenation, cleanliness, reduced stocking density) combined, if necessary, with antifungal treatments suited to the aquatic environment, applied under specialist supervision. Stress reduction and isolation of affected fish are integral to management.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Maintaining good water quality with sufficient turnover and appropriate filtration greatly reduces risk. Avoiding overstocking in tanks or farming structures reduces collective stress. Gentle handling during transport or sorting after capture prevents gill injuries that serve as entry points. Regular monitoring of gill condition allows early detection.
Possible complications
Without intervention, progressive destruction of gill tissue severely compromises gas exchange, potentially leading to respiratory failure. Secondary bacterial infection may develop on fungal lesions, worsening the prognosis. Mortality can occur with extensive involvement or delayed management.
When to see a veterinarian
The fish breathes abnormally fast or stays near the surface. The gills appear discolored, damaged, or covered with unusual deposits. The fish refuses to eat for several days. Lethargy or erratic swimming is observed. Multiple fish in the same tank show similar signs.
Prognosis
The outlook depends on how quickly treatment begins and how much of the gills are affected. An infection caught early and managed with improved farming conditions has a good chance of recovery. However, extensive or neglected gill disease can be fatal, since the gills are essential for the fish's survival.
Frequently asked questions
Can hake's gill mycosis be transmitted to other fish?
Yes, in the same tank or farming area, the fungi responsible can spread from one weakened fish to another, especially if the water quality is poor.
Does this disease also affect wild hake?
It is mainly documented in captivity or under high-stress conditions; in wild populations in open ocean, it remains rarely reported but not impossible if the fish is weakened.
Can you eat hake affected by this fungus?
A visibly sick fish with gill lesions should not be consumed; it is preferable to discard it as a precautionary health measure and to consult a professional.
How can I prevent this disease from appearing in a hake farm?
Water quality, reasonable fish density, and careful handling are the best means of prevention.
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 23 August 2026
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