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Intestinal cestode infestation of the manta ray
Intestinal cestode infestation affects manta rays (Mobula birostris), both in the natural environment and in public aquariums. Cestodes are flatworms, commonly called "tapeworms", which live attached to the wall of the spiral intestine of t...
What is it?
Intestinal cestode infestation affects manta rays (Mobula birostris), both in the natural environment and in public aquariums. Cestodes are flatworms, commonly called "tapeworms", which live attached to the wall of the spiral intestine of the skate using attachment organs called scolex. They feed on nutrients already digested by the animal, which deprives the ray of part of its diet. This parasitosis is regularly encountered in manta rays kept in tanks, where they are more easily detected during routine checks or autopsies.
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:
Many manta rays carrying cestodes show no visible signs, especially if the infestation remains moderate.
When the parasitic load becomes significant, we can observe progressive weight loss despite a normal or reduced appetite.
The stingray may appear less vigorous, swim less dynamically, or remain still more often.
Stools may become softer or change in appearance, but this sign is difficult to observe in the natural environment.
In severe cases, marked weight loss with an angular silhouette may appear, particularly at the base of the tail and behind the head.
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 infestation is due to cestodes (segmented flatworms) which colonize the spiral intestine, the characteristic digestive organ of rays and sharks. Several species of cestodes may be involved depending on the geographical area. These worms have a complex life cycle often involving intermediate hosts, such as small crustaceans or other marine invertebrates, which the skate ingests by feeding on plankton through filtration.
Manta rays feeding by filtration on large quantities of plankton are exposed to the larval stages of cestodes present in their food.
Individuals kept in captivity may present infestations linked to water quality, stress or a diet containing contaminated intermediate hosts.
A weakened immune system, for example during chronic stress or concomitant illness, favors the establishment and multiplication of parasites.
Young, actively growing individuals may be more sensitive to the nutritional consequences of infestation.
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 direct observation of worm segments or eggs during examination of feces under a microscope, carried out by a veterinarian specializing in aquatic animals.
In some cases, endoscopy or imaging may be considered to view the inside of the digestive tract.
Accurate identification of the cestode species may require sending samples to a laboratory specializing in marine animal parasitology.
Monitoring the animal's weight curve and eating behavior completes the clinical evaluation.
Treatment
The treatment is based on the administration of antiparasitics belonging to the anthelmintic family, chosen and dosed exclusively by a specialized veterinarian, taking into account the volume of water and the particular sensitivity of the rays.
Nutritional support may be offered at the same time to help the animal replenish its body reserves during treatment.
Post-treatment monitoring generally includes new parasitological checks to verify the effectiveness of the treatment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
In captivity, regular monitoring of the health and weight of rays allows suspicious weight loss to be identified early.
The quality of the water and the controlled origin of the food distributed reduce the risk of introducing parasites.
Routine parasitological examinations, particularly on stools, can be offered by veterinary teams specializing in aquariums.
In the natural environment, no prevention is really applicable, the infestation being part of the normal ecological cycle of the species.
Possible complications
A large and prolonged infestation can lead to chronic malnutrition, lowered general immunity and greater susceptibility to other diseases.
In already weakened animals, the combination of several parasites or infections can worsen the general condition and compromise the prognosis.
When to see a veterinarian
Visible weight loss or loss of muscle mass in a manta ray monitored in captivity.
Noticeable change in swimming behavior or usual activity.
Presence of worm segments or abnormalities in the stools observed during pool cleaning.
Persistent decrease in appetite with no other identified cause.
Prognosis
The prognosis is generally favorable when the infestation is detected and treated at an early stage, particularly in captivity where monitoring is regular.
In the event of a massive infestation and delay in treatment, the general weakening can more seriously compromise the health of the animal.
Frequently asked questions
Can manta ray cestodes be transmitted to humans?
No, the cestodes which parasitize the intestines of manta rays are specific to cartilaginous fish and do not represent a known risk to humans.
How does a manta ray catch cestodes?
By feeding by filtration of plankton, the ray can ingest small organisms which carry the larvae of the parasite, which allows the cestode to settle in its intestine.
Can an infested manta ray continue to feed well?
Yes, in many cases the appetite remains normal, especially at the beginning. It is often the progressive weight loss that puts you on alert, more than the refusal to eat.
Can we prevent this infestation in a manta ray in an aquarium?
We can reduce the risk by controlling the quality of the water and the origin of the supply, but we cannot guarantee total prevention; Regular veterinary monitoring remains essential.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 11 August 2026
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