Megamouth Shark Gill Fungus
The megamouth shark (Megachasma pelagios) is an extremely rare species of large planktivorous shark living in deep waters, first discovered in 1976. Fewer individuals have ever been observed or studied than any comparable shark species, whe...
What is it?
The megamouth shark (Megachasma pelagios) is an extremely rare species of large planktivorous shark living in deep waters, first discovered in 1976. Fewer individuals have ever been observed or studied than any comparable shark species, whether in the wild or in captivity.
Because of this extreme rarity, there is virtually no documented scientific data on a gill fungus specific to this species. Fungal infections of the gills are, however, documented in other species of cartilaginous and bony fish, particularly in captivity or when exposed to significant stress, injury, or poor water quality.
This sheet should therefore be read as a cautious extrapolation from general knowledge about fungal gill infections in fish, applied by analogy to the megamouth shark, given the lack of species-specific literature available.
Key point
The megamouth shark is an extremely rare and poorly understood species; any severe respiratory disease in an individual, whether wild or in captivity, holds major scientific and conservation significance beyond the clinical concern for that individual alone.
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 expected signs, by analogy with other cartilaginous fish affected by gill fungus, would be visible respiratory distress (abnormally rapid or irregular gill movements), slowed or erratic swimming, loss of appetite, and general weakness.
Visible changes to the gills (abnormal color, deposits, damaged tissue) might be observed if the animal can be examined closely, which remains exceptional for this deep-water species and is rarely maintained in captivity.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Fungal gill infections in fish are typically caused by opportunistic fungi (such as certain species of Saprolegnia or other aquatic fungi) that colonize gill tissue already weakened, for example after an injury, stress from transport or capture, or exposure to degraded water quality.
No specific cause has been formally documented in the megamouth shark owing to the extremely small number of individuals ever studied.
Stress from accidental capture, transport, captive holding unsuited to the physiological needs of a deep pelagic species, poor water quality, or preexisting gill injury could promote opportunistic fungal infection, by analogy with other large sharks.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Diagnosis would rely on direct observation of the gills, ideally supplemented by sampling for mycological analysis at a specialized laboratory to identify the fungal agent(s) involved and rule out other causes (bacterial, parasitic).
Given the extreme rarity of the species, any suspected case should immediately involve a veterinary team specializing in exotic aquatic animals and, if possible, experts in deep-sea shark biology.
Treatment
By analogy with other fish, treatment would involve antifungal medications suitable for aquatic environments, combined with strict improvement of water quality. No validated therapeutic protocol exists specifically for this species.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Should any attempt be made to keep this species in captivity (extremely unusual for this species), maintaining optimal water quality, minimizing stress and handling, and providing close veterinary oversight would be the most relevant prevention measures, extrapolated from best practices in large shark aquaculture.
Possible complications
Severe gill involvement could seriously compromise gas exchange and lead to potentially fatal respiratory distress, as documented in other fish with advanced gill fungal infections.
When to see a veterinarian
Abnormally rapid or irregular breathing movements.
Slowed, disoriented swimming or pressing against tank walls.
Prolonged loss of appetite.
Any visible alteration of gill tissue.
Prognosis
A reliable prognosis cannot be established for this species due to lack of documented cases. In other fish, the outlook for gill mycosis depends heavily on how early treatment is started and the animal's overall condition.
Frequently asked questions
Are there confirmed cases of branchiomycosis in the megamouth shark?
No, to date no clinically documented cases have been published. This fact sheet is based on general knowledge concerning branchial mycoses in fish, due to the lack of species-specific data for this very rare species.
Can the megamouth shark be treated in captivity?
This species is almost exclusively observed in deep natural environments. Rare attempts to keep it in captivity have been of very short duration, making any veterinary treatment extremely difficult to implement.
Is a gill fungus transmissible to other fish or to humans?
Fungi responsible for gill mycosis in fish are not considered zoonotic. However, a risk of transmission to other fish in the same tank cannot be excluded in confined environments.
What to do if a megamouth shark is observed in respiratory distress in the wild?
It is advisable to contact the competent scientific or marine conservation authorities immediately, as each observation of this species is of exceptional scientific value.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 07 September 2026
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