Thresher shark pneumonia

What is it?

“Thresher shark pneumonia” is a general public term used to describe respiratory damage affecting the gills of this shark. In fish, there are no lungs: the respiratory function is carried out by the gills. We are therefore more accurately speaking of gill inflammation or infection which disrupts gas exchange and oxygenation of the animal. This condition remains poorly documented in the thresher shark (Alopias vulpinus), a pelagic species difficult to observe and maintain in captivity. The available information mainly comes from extrapolation from other species of sharks and marine fish. It can occur in the natural environment, but it is mainly reported in captivity (aquariums, research structures), where stress and promiscuity favor infections.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Causes and risk factors

Several agents may be involved: opportunistic bacteria naturally present in seawater (notably certain Gram-negative marine bacteria), more rarely fungi or gill parasites which weaken the tissue and open the door to bacterial superinfection.

Stress linked to capture, transport or an unsuitable environment often plays a triggering role by weakening the animal's immune defenses.

Degraded water quality (poor oxygenation, unsuitable temperatures, high levels of organic matter or ammonia) is the main risk factor.

The stress of capture or transport, promiscuity in a tank, prior injury to the gills, as well as an immune system weakened by another disease increase the animal's vulnerability.

The thresher shark, a pelagic species and very active in the natural environment, does particularly poorly in confinement, making it a high-risk species in captivity.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

Treatment

Treatment is based, depending on the cause identified, on antibacterial, antifungal or antiparasitic treatments administered by means adapted to the aquatic environment.

Immediate improvement in water quality and reduction of environmental stress are an integral part of treatment, in addition to any drug treatment.

Prevention

Possible complications

Severe gill damage can lead to progressive respiratory failure, general exhaustion and, if left untreated, a risk of mortality.

Secondary bacterial superinfection or septicemia (generalized infection) may also occur if the animal's general condition deteriorates.

When to see a veterinarian

Prognosis

The prognosis largely depends on how early treatment is received and the underlying cause. An attack detected early and associated with a rapid improvement in environmental conditions has a better chance of a favorable outcome.

In the absence of intervention, the evolution may be unfavorable due to the difficulty in treating this fragile species and poorly adapted to captivity.

Frequently asked questions

References

WOAH — Organisation mondiale de la santé animale (ex-OIE)

Content reviewed by the TunisieVet editorial team · Updated 24 September 2026