Gastrointestinal parasitism of sawfish (roundworms)
Gastrointestinal parasitism caused by roundworms (nematodes) is a common digestive condition in sawfish, a cartilaginous fish related to rays. These parasites live in the stomach or intestine of the animal and feed at the expense of its hos...
What is it?
Gastrointestinal parasitism caused by roundworms (nematodes) is a common digestive condition in sawfish, a cartilaginous fish related to rays. These parasites live in the stomach or intestine of the animal and feed at the expense of its host. This disease affects both wild sawfish and those kept in public aquariums or ponds, particularly when breeding conditions favor the parasitic cycle.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
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The signs are often discreet and not very specific, which makes the disease difficult to spot without a veterinary examination.
We may observe a fish that eats less or refuses food, a gradual loss of weight despite a sometimes retained appetite, and swimming less active or slower than usual.
The belly may appear swollen or distended in certain individuals. Abnormally soft or discolored stools are sometimes noted. In severe infestations, worms may be visible in the faeces or, more rarely, regurgitated.
In severe cases, marked weight loss and a weakened general condition gradually set in.
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 the presence of nematodes (roundworms) in the digestive tract, particularly the stomach and intestine. Several genera of nematodes are known to parasitize marine cartilaginous fish, including sawfish. These parasites generally have a life cycle involving one or more intermediate hosts, often marine invertebrates (crustaceans) or small fish, which the sawfish ingests while feeding.
Young sawfish and weakened or stressed individuals are more sensitive to a significant infestation.
A diet based on live prey or uncontrolled whole fish increases the risk of ingesting parasitic larvae.
Poor water quality, too high a population density in a pond, or chronic stress linked to transport or captivity can weaken the animal's natural defenses and promote the development of the parasitism.
The absence of quarantine before the introduction of new animals or new prey into a breeding system is also a significant risk factor.
Transmission
Transmission occurs mainly by ingestion of prey (small fish, crustaceans) carrying nematode larvae. Direct transmission between fish without an intermediate host is generally unlikely, but depends on the exact parasite cycle involved.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The diagnosis is based on a complete clinical examination carried out by a veterinarian specializing in aquatic or exotic animals.
Examination of stools (coproscopic analysis) makes it possible to look for eggs or fragments of worms. In some cases, endoscopy or imaging tests may be offered to visualize the digestive tract.
If the animal dies, a post-mortem examination (necropsy) can confirm the diagnosis by directly identifying parasites in the digestive tract.
Treatment
Treatment is based on the use of antiparasitic medications (dewormers) suitable for fish, prescribed and dosed only by a veterinarian competent in aquatic animal medicine.
Supportive measures, such as improving water quality and adjusting the diet, usually accompany drug treatment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention is based above all on good management of food and the environment.
It is recommended to control the origin of the prey given to sawfish in captivity, favoring reliable sources and if possible frozen, which reduces the risk of transmission of live larvae.
A quarantine of new animals and regular parasitic monitoring by stool examinations make it possible to detect an infestation before it becomes severe.
Maintaining a good water quality and appropriate breeding density limits stress and strengthens the natural resistance of fish.
Possible complications
A large, untreated infestation can lead to intestinal obstruction, chronic inflammation of the digestive tract, severe weight loss and general weakening of the animal, making it more vulnerable to other infections.
When to see a veterinarian
The fish has refused to eat for several days.
Weight loss or visible weight loss is observed.
Worms are observed in the stools or in the pond water.
Swimming behavior becomes abnormal or lethargic.
The belly appears unusually swollen.
Prognosis
The prognosis is generally favorable if the infestation is detected early and treated appropriately by a specialist veterinarian. Without treatment, severe infestations can compromise the general health of the animal, particularly in young or already weakened individuals.
Frequently asked questions
Is sawfish gastrointestinal parasitism transmissible to humans?
No, these roundworms specific to fish are not considered transmissible to humans under usual conditions.
How does a sawfish catch these worms?
Generally by consuming prey (small fish, crustaceans) which harbor nematode larvae in their body.
Can we see worms with the naked eye?
In large infestations, worms may sometimes be visible in the stool, but a veterinary examination is still necessary to confirm the diagnosis.
Should an infested sawfish be isolated from other animals in the pond?
This depends on the parasite cycle and should be assessed by a veterinarian, as direct transmission between fish without an intermediate host is generally limited.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 30 October 2026
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