parasitic disease Mako shark

Gastrointestinal parasitism in shortfin mako sharks (roundworms)

Gastrointestinal parasitism in shortfin mako sharks refers to the presence of roundworms (nematodes) in the stomach, pylorus, or spiral intestine of this pelagic shark. These parasites naturally occur in many wild cartilaginous fish, includ...

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

Gastrointestinal parasitism in shortfin mako sharks refers to the presence of roundworms (nematodes) in the stomach, pylorus, or spiral intestine of this pelagic shark.

These parasites naturally occur in many wild cartilaginous fish, including mako sharks in the open ocean.

The condition becomes a genuine disease especially when an animal is kept in an aquarium or tank under stress or weakened conditions, allowing parasites to proliferate.

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:

Loss of appetite Weight loss Vomiting Soft stools Hard or painful abdomen Fatigue Abnormal swimming

Signs are often subtle at first, as sharks conceal pain and illness well.

Reduced appetite or food refusal may be observed, along with progressive weight loss despite apparently normal feeding, and less vigorous or more erratic swimming.

Regurgitation or vomiting of poorly digested prey is sometimes seen, as well as abnormally soft or stringy stools.

In advanced cases, the animal may appear listless, staying near the bottom of the tank, and show abdominal tenderness if examined.

Some heavily infested individuals develop relative anemia, visible as pale gills or mucous membranes.

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 gastrointestinal nematodes, notably species from the Anisakidae family or related groups, which naturally parasitize many sharks and marine fish.

The life cycle of these worms generally involves intermediate hosts such as small crustaceans, then fish or cephalopods, before reaching the shark, the definitive host, when it consumes these infected prey.

In the wild, a moderate parasitic burden is tolerated without visible consequence.

Problems arise when this balance is disrupted: capture stress, transport, confinement in a tank, inappropriate feeding, or immunosuppression then favor parasite multiplication and symptom development.

Recently captured mako sharks or those transferred to care facilities are most at risk, due to the substantial stress this species tolerates poorly.

Feeding on raw, uncontrolled fish or cephalopods increases the risk of introducing new parasites.

Restricted swimming space, poor water quality, or insufficient oxygenation weaken the animal and promote parasitic proliferation.

Young individuals and those already weakened or injured are also more susceptible.

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 examination of the animal when possible, supplemented by analysis of feces or regurgitated material to look for eggs or worms.

In a captive animal, a blood panel can help evaluate overall effects, such as anemia or signs of inflammation.

In some cases, digestive endoscopy performed by a veterinarian specialized in aquatic animals allows direct visualization of parasites in the stomach.

Post-mortem examination unfortunately remains often the most reliable way to confirm heavy infestation, particularly in stranded wild animals.

Treatment

Treatment, when possible, is based on administering antiparasitic drugs from the anthelmintic family, specifically chosen and tailored by a veterinarian experienced with aquatic species.

Nutritional support and improvement of captive conditions systematically accompany medical treatment.

This type of care remains rare and highly specialized, reserved for a few facilities worldwide with the necessary expertise on this pelagic species that is difficult to maintain in captivity.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Prevention relies above all on careful food management, using controlled prey that is frozen or treated to limit the intake of live parasites.

Minimizing handling and transport stress is essential, as the shortfin mako shark is particularly sensitive to stress, which can worsen any underlying disease.

Optimal water quality, regular veterinary monitoring, and routine parasite screening in captive animals allow early detection of abnormal parasite loads.

In the wild, prevention is neither possible nor necessary, as parasitism is part of the normal ecology of the species.

Possible complications

Massive untreated infestation can lead to intestinal obstruction, lesions of the stomach or intestinal wall, or even perforation in extreme cases.

Chronic weight loss and malabsorption can result in general weakness that favors other opportunistic infections.

In an animal already weakened by captivity, these complications can contribute to a fatal outcome, as the shortfin mako shark is known for its fragility in artificial environments.

When to see a veterinarian

Prolonged refusal to eat or marked decrease in appetite

Visible weight loss despite apparent eating

Abnormal swimming, lethargy, or unusual positioning in the tank

Repeated vomiting or regurgitation

Soft, filamentous, or abnormal feces

Paleness of the gills or visible mucous membranes

Prognosis

Prognosis depends strongly on how early treatment is started and on the intensity of the infestation.

A light to moderate parasite load detected early in an otherwise healthy animal has a favorable prognosis with appropriate management.

Conversely, in a shortfin mako shark already weakened by captivity stress, prognosis remains guarded, as this species is known for its difficulty adapting to artificial environments and its high sensitivity to stress and disease.

Frequently asked questions

Is gastrointestinal parasitism dangerous for a wild shortfin mako shark?

No, in natural environments a moderate parasite load is normal and well tolerated. The problem mainly arises in stressed, weakened animals or those kept in captivity.

Can you see the worms directly in the basin water?

It's possible if the animal regurgitates or expels worms in its feces, but most of the time parasites remain invisible without specialized examination.

Is this disease transmissible to humans?

No, these nematodes are specific to marine fish and do not pose a direct transmission risk to humans in this context.

Can the mako shark be treated as a standard aquarium fish?

No, it is a pelagic species that is highly demanding and fragile in captivity, requiring treatment by a veterinarian with highly specialized expertise in marine aquatic species.