Parasitism by copepods and crustaceans parasitic on the torpedo ray
Torpedo rays (Torpedo torpedo, Torpedo marmorata) can host various small parasitic crustaceans, mainly copepods, which live attached to their skin, their gills or their fins.\nThese parasites belong to well-known groups of cartilaginous fis...
What is it?
Torpedo rays (Torpedo torpedo, Torpedo marmorata) can host various small parasitic crustaceans, mainly copepods, which live attached to their skin, their gills or their fins.\nThese parasites belong to well-known groups of cartilaginous fish such as sharks and rays, for example certain siphonostome copepods specialized in the skin of selachians.\nThis parasitism is especially observed in torpedo rays kept in captivity, in public aquariums or breeding structures, but it also exists in the wild.\nThe presence of a few parasites does not necessarily lead to visible disease, but a significant infestation can weaken the animal.
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 signs are not always easy to spot in an aquatic animal.\nWe can observe small threadlike or rice-grain-shaped organisms clinging to the skin, the fins or near the gill slits.\nThe ray may rub against the sand, rocks or the walls of the pool to try to get rid of the parasites.\nSlower swimming, periods of unusual inactivity or a withdrawal to the bottom of the pool are possible.\nIn more severe cases, we may see irritated, slightly damaged or discolored areas of skin, as well as a fin with a frayed edge.\nA decreased appetite may accompany a significant infestation, especially if the gills are affected.
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 due to the attachment of parasitic crustaceans, most often copepods, to the skin or gills of the torpedo ray.\nThese parasites feed on the mucus, skin debris or blood of their host using adapted mouthparts.\nCertain species remain permanently attached, others move more on the surface of the body.\nThe introduction of new fish or rays not quarantined into a tank is a frequent source of contamination.
Poor quality or poorly filtered water encourages the development of parasites.\nA high density of animals in the same pool increases the risk of transmission between individuals.\nThe absence of quarantine for new arrivals in an aquarium or a breeding facility is a major risk factor.\nAn animal already weakened, stressed by transport or by unsuitable breeding conditions, tolerates the presence of parasites less well.\nWater temperatures unusual for the species can also play a favorable role.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian specializing in aquatic or exotic animals examines the animal, if possible with minimal handling to limit stress.\nHe can take a visible parasite to identify it under a microscope.\nAn examination of the skin and gills, sometimes supplemented by a skin scraping, helps to confirm the diagnosis and estimate the intensity of the infestation.\nThe parameters of the pond water are generally checked in parallel, because they influence the prognosis and the choice of treatment.
Treatment
Treatment is based on antiparasitics suitable for cartilaginous fish, to be used only under the supervision of a specialist veterinarian.\nStingrays and other selachians are particularly sensitive to certain molecules commonly used in bony fish, which requires great caution in the choice of product.\nMedicated baths or treatments added to pond water may be offered depending on the case.\nImproving water quality and reducing stress are an integral part of the treatment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
The systematic quarantine of any new animal before its introduction into a common pool is the most important measure.\nRegular monitoring of water quality, particularly its filtration and its physicochemical parameters, limits the development of parasites.\nRegular observation of the skin and fins allows early detection.\nAvoiding overpopulation in pools reduces the spread from one animal to another.\nDisinfect and carefully rinse any transferred material or decoration from one pool to another is also recommended.
Possible complications
A large, untreated infestation can lead to secondary skin lesions, which opens the door to bacterial or fungal infections.\nParasites attached to the gills can interfere with breathing if their numbers are high.\nA weakened animal becomes more susceptible to other diseases and may show progressive weight loss.
When to see a veterinarian
Presence of small organisms visible on the skin, fins or near the gills.\nRepeated rubbing against the decor or floor of the pool.\nAbnormal, slowed swimming or unusual inactivity.\nLoss of appetite or refusal of food.\nSkin lesions, discoloration or damaged fins.
Prognosis
The prognosis is generally favorable when the infestation is detected early and treated by a competent aquatic animal professional.\nA severe infestation, especially if the gills are affected or if infectious complications appear, can worsen the prognosis.\nThe quality of the water and the speed of treatment are determining factors for recovery.
Frequently asked questions
Can these parasites be transmitted to other fish in the pond?
Yes, some parasitic copepods can spread to other fish or rays sharing the same tank, especially if the water is poorly filtered or the animal density is high. This is why the quarantine of new arrivals is essential.
Can we see parasites with the naked eye?
Some copepods of sufficient size are visible to the naked eye, appearing as small filaments or grains clinging to the skin. Others are more discreet and require close examination or sampling to be identified.
Is the treatment risky for the torpedo ray?
Rays and other cartilaginous fish are more sensitive than bony fish to certain antiparasitic drugs. Treatment should therefore always be chosen and monitored by a veterinarian familiar with exotic aquatic animals.
Can a wild torpedo ray have these parasites without being sick?
Yes, low numbers of parasites are often tolerated without visible clinical signs in nature. It is mainly a massive infestation or a weakened animal that causes symptoms.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 25 September 2026
Comments (0)
No comments yet.
AT A GLANCE
Need a veterinarian?
Find a practitioner near you on TunisieVet, with their specialities, hours and contact details.
Find a veterinarianCategories
Affected species
This information is provided for educational purposes only and is not a substitute for a veterinary consultation. If you have any concerns about your animal's health, consult a veterinarian.
Thinking of welcoming a pet? Dogs and cats are waiting for a family in Tunisia, and adoption is completely free.
Adoption listingsTo discover
Related diseases and linked Animalia content.
Gastrointestinal parasitism of the torpedo ray (roundworms)
Parasitic
Bacterial skin infection of the torpedo ray
Bacterial
Bacterial skin ulcerations of the torpedo ray
Bacterial
Gill mycosis of the torpedo ray
Fungal
TunisieVet in your pocket 📱🐾 Access your veterinary services wherever you are. [ Download the app ]
Learn more