Raising Healthy Motoro Stingrays: Size, Diet, and Environment

Motoro stingray (Potamotrygon motoro) is one of the most famous and popular freshwater stindrays. We should mention that despite the motoro stingray popularity in aquarium husbandry, there is still no quite precise classification of this family representatives. From time to time, some new kinds are discovered, which were not described before.

Habitat in the wild

The Motoro Stingray (Potamotrygon motoro) is a species of freshwater stingray that belongs to the family Potamotrygonidae. The Potamotrygonidae family, commonly known as river stingrays or Neotropical freshwater stingrays, is a group of cartilaginous fish found in South America.

These stingrays are adapted to live in various freshwater habitats such as rivers, streams, and flooded areas. They have a flattened body shape, wide pectoral fins that resemble wings, and a long tail armed with one or more venomous spines for defense.

Motoro stingrays, like other members of the Potamotrygonidae family, are primarily bottom-dwelling carnivores. They feed on a diet of small aquatic animals such as crustaceans, insects, mollusks, and small fish.

This kind is quite widespread in South America. The ocellate river stingray is also encountered in Colombia, Peru, Bolivia, Brazil, Paraguay, and Argentina. Motoro stingray inhabits both Amazon River and its tributaries: Orinoco, Rio-Branko, Parana, Paraguay rivers.

Like other representatives of the kind, the freshwater stingray is encountered in different biotopes. Mainly these are sandbanks of large rivers and their tributaries where the substrate consists of mud and sand.

During the rainy season, this freshwater stingray moves to flooded forests and during the dry season – to the lakes that were formed earlier.

Scientific NamePotamotrygon motoro
Common NameMotoro stingray; ocellate river stingray; motoro ray; freshwater stingray; peacock-eye stingray; black river stingray; motoro fish
HabitatFreshwater rivers, streams, and flooded areas
Geographic RangeSouth America (Amazon River basin and surrounding areas)
Body ShapeFlattened and disc-like
SizeUp to about 16 inches (40 cm) in diameter
ColorationUsually brown or gray with distinctive markings
Pectoral FinsLarge, wing-like fins used for swimming and gliding
TailLong, slender, and equipped with venomous spines
DietCarnivorous; feeds on small aquatic animals
Venomous SpinesYes; used for defense
BehaviorGenerally peaceful, but may become aggressive if threatened
Aquarium RequirementsLarge tank with sandy substrate, strong filtration, and hiding spots
Water ParametersTropical freshwater; temperature around 75-82°F (24-28°C) and neutral to slightly acidic pH
Tank SizeMinimum 125 gallons (473 liters) for a single stingray
CompatibilityGenerally should be kept with peaceful tank mates
HandlingRequires careful handling due to venomous spines
Conservation StatusNot Evaluated (IUCN Red List)


Rays are relatives of sharks and sawfishes, which have a skeleton that differs from the one that ordinary fishes have, since it doesn’t have bones, and it completely consists of cartilageous tissue.

Poisonous spine

The scientific name of this kind is an ocellate river stingray, which means that the ray can sting. Really, the motoro ray has a poisonous spine on its tail (actually, it used to be a scale once). The ray uses this spine to protect itself. The poison is produced by the glands located near the bottom of the spine.

The venomous spine serves as a defensive mechanism for the stingray. When threatened or disturbed, the stingray can arch its tail and use the spine to deliver venom to potential predators or perceived threats. The venom can cause intense pain, swelling, and in some cases, it can be harmful or even fatal to humans.

Contrary to common belief, rays don’t attack humans with their spines. You should step on one of them or disturb somehow to make the fish sting you. Motoro stingray loses its spine occasionally (every 6-12 months), and you can find it on the bottom of the tank. This is a normal situation, and it shouldn’t bother you.

It’s important to handle stingrays, including motoro stingrays, with extreme care and avoid touching the tail to prevent getting stung. If you ever encounter a stingray in the wild or while diving, it’s best to observe them from a safe distance and avoid any actions that might provoke them.

For those who keep motoro stingrays or other stingray species in aquariums, it is crucial to understand their behavior and take necessary precautions to avoid accidental stings. Always use appropriate tools and techniques when handling or maintaining the aquarium to ensure the safety of both the stingray and the keeper.

Ampullae of Lorenzini

Another feature of freshwater stingrays is the ampullae of Lorenzini. This is a special tube or channel located on the fish head (around its eyes and nostrils). Using these, cartilaginous fishes detect electric fields, and they help them to navigate according to the terrestrial magnetic field.


Motoro stingrays are relatively small compared to some other species of stingrays. In the wild, motoro stingray is up to 50 cm large in diameter and up to 1 m long. It weighs up to 35 kilos. When keeping it in the tank, the fish, of course, doesn’t grow that large. They typically reach a maximum size of around 12 to 14 inches (30 to 35 centimeters) in disc width, which is the measurement across the body from one pectoral fin to the other. The total length, including the tail, can be up to 2 feet (60 centimeters) or slightly more.


On average, in captivity, motoro stingrays can live anywhere from 8 to 15 years, but some individuals have been known to live longer with excellent care and optimal conditions.


The motoro ray is disk-shaped, and the disk is almost round. The fish eyes are updrawn above its back. The latter is usually beige or brown colored with numerous marigold yellow spots and dark circles.


The motoro ray abdomen is white. The color and location of the spots may significantly vary from one fish to another. In the Amazon river basin, there were defined three basic coloring types of stingrays, but each of them includes several subtypes.

Difficulties in keeping

It’s important to note that keeping motoro Sstingrays or any other stingrays as pets requires a considerable amount of knowledge, effort, and dedication. They have specific care requirements and need a large, well-maintained aquarium with appropriate filtration and water conditions. Furthermore, their venomous spines require careful handling to avoid injury to both the stingray and the keeper. Always make sure to research thoroughly and seek advice from experienced aquarists or experts before considering keeping a stingray as a pet.

Ocellate river stingray is one of the most popular representatives of the kind among the aquarists. Many of them get very surprised when they find out that some rays dwell in freshwaters.

Freshwater rays are rather clever, and they can interact with humans. You can even train them to hand-feed. Nevertheless, motoro stingray is not for everyone. It requires large tanks, perfect conditions, and a special diet.

But for those who are ready to put efforts to keep a ray in a tank, the motoro stingray will become a unique and the most loved pet. In the past, most rays on sale were caught in the wild. It means that they were quite stressed as well as brought some parasites and illnesses with them. Most rays sold nowadays were bred in captivity.

This motoro stingray is dangerous. Most locals in the countries where rays dwell are afraid of this fish more than of other life-threatening species such as piranha. For instance, in Columbia, annually, more than 2000 cases of injuries and even accidental deaths as a result of ray attacks are registered.

The poisonous spine is located on top of the ray’s caudal fin, where you can clearly see it. It is covered with a thin outer cover that serves to protect the ray itself from its poisonous glands.

The internal spine surface has a row of reverted spines. They help to tear the cover when the ray uses its spine and to widen any wound it makes. These spines direction also allows using them as a fly-hook, which makes it harder to remove them from the wound.

Although toxic properties of poisons of various ray kinds may differ, their composition, in general, is alike. The poison is based on proteins and has a cocktail of chemicals aimed to cause both severe pain and fast tissue degeneration (necrosis).

If a motoro ray has stung you, be prepared for severe pain on the bite site and headache, nausea, and diarrhea. You should visit a doctor regardless of how strong the symptoms are.

It goes without saying that when keeping rays in a tank, you should be extremely careful. However, the chances of being stung are very low if you behave respectfully. As a rule, these are not aggressive fishes, and they use their spine only as a protection measure.

Actually, rays become very domestic; they learn to recognize their owner and come to the water surface to ask for food. Most injuries happen when reckless owners try to ‘stroke’ the motoro stingray or catch it with a scoop-net.

You should never use it for this purpose. It’s better to take some solid container instead.

Keeping in a tank

Water parametrs

Freshwater rays are very sensitive to ammonia, nitrites, and nitrates content in water, that’s why it is important to have an understanding of a nitrogen cycle and keep the tank water crystal clear.

The latter is quite a challenging task since rays produce a large amount of ammonia. Large-sized tanks, efficient biological filtration, and regular water renews – is the only way to keep the proper tank and water conditions.

Most freshwater rays can be kept in a tank at PH from 6,8 to 7,6, alkalinity from 1° to 4° (from 18 to 70 ppm) and water temperature from 24 to 26°C. Ammonia and nitrites level should be zero, and nitrates level should be lower than 10 ppm.

Tank size

Potamotrygon motoro require a large and adequately sized aquarium due to their active and growing nature. As these stingrays can reach a disc width of up to 18-24 inches (45-60 cm) and have long tails, it’s essential to provide them with ample space to swim and move comfortably.

In terms of the tank size for rays, the following approach works best – the larger, the better. The walls height is not a crucial parameter, but the tank should be from 180 to 220 cm long and from 60 to 90 cm wide to keep a motoro ray in it for a long time.

A minimum tank size of around 180 to 250 gallons (680 to 950 liters) is often recommended for a single motoro stingray, but for a long-term keeping of adult species, you will need a tank not less than 1000 liters large.

If you plan to keep multiple motoro stingrays or other fish in the same tank, you’ll need an even larger aquarium. As a general rule, add at least 75 to 100 gallons (280 to 380 liters) for each additional stingray to accommodate their territorial and swimming needs.


The substrate for a motoro stingray aquarium should be carefully chosen to mimic their natural habitat and promote their well-being. Since stingrays are bottom-dwelling fish, the substrate plays a crucial role in providing a comfortable and safe environment for them.

The ideal substrate for a motoro stingray aquarium is fine sand. Sand is preferred because it allows the stingrays to bury themselves partially, which is a natural behavior for them. They use this behavior to hide, rest, and feel secure. The sand should be soft and free of any sharp or abrasive particles that could potentially injure the stingray’s delicate underside.

Avoid using gravel or large pebbles, as these can be uncomfortable for the stingray to move over and may also pose a risk of injury. Additionally, larger substrate materials can trap debris and make it more challenging to maintain a clean aquarium.

Before adding the sand to the aquarium, it should be thoroughly rinsed to remove any dust or impurities. A layer of around 2 to 3 inches (5 to 7.5 centimeters) of sand is typically sufficient for a motoro stingray tank.

Another option is not to use the substrate at all. This simplifies the tank maintenance but makes it look a bit severe and unnatural. Besides, rays like digging into the sand when they are stressed out, and usually in the wild, they dwell in waters with sandy or muddy bottom. Thus, it seems quite cruel to let them live without having a chance to find shelter in the tank.


As for the tank decorations, they should be smooth without any sharp edges. Actually, tank decorations are not really necessary in a tank with rays. However, you can put some large snags or smooth stones, if you like.

Leave as much as possible free space for the motoro stingray to swim, to let them move and dig into the sand. Heaters should have protection around them or put them out of the tank to ensure that the rays won’t get burnt.

There should be some dim light with a 12-hours cycle (day/night). The motoro stingray will eat tank plants that require rooting in the substrate, but you can try some plants that can be fixed to the decorations such as java moss or Anubias spp.

However, even these may not survive the fish’s attention.


Freshwater rays are flesh-eaters that feed mainly with fish and crustaceans in the wild. These are active fishes with high metabolism level, and that’s why you should feed them at least twice a day. They are also known as gluttonous ones, thus the food for them will be quite costly for you. In general, the motoro stingray diest should be natural, though some may eat artificial food.

Young species eat live or frozen blood worm, tubifex, brine shrimps, prawns, etc., while adult ones should be fed with the food of larger size. It can be whole mussels, shellfishes, prawns, calamaries or fish juveniles (or some other fresh fish), and earthworms. Diverse diest is a must to keep the motoro stingray in its best condition.

After you buy a motoro stingray, it often eats quite unwillingly, and it’s not in the best shape as well. It must start eating as fast as possible because of its fast metabolism. Blood and earthworms (the latter can be cut in small pieces) are considered the best food to help the motoro ray adapt to new tank conditions.

They shouldn’t be fed with flesh from mammals such as ox heart or chicken. The motoro stingray can’t properly digest some of the lipids that this meat contains, and this may cause excessive lipopexia and even some organs necrosis.

Also, there is no use it feeding it with some edible fish, such as livebearers or small goldfish. Such a diet may be the reason for the possible spread of illnesses and parasites.

Tank mates

Rays spend most of their time on the bottom. Their eyes and branchial apertures are on top of the body, which allows the fish to spend time under the sand waiting for food. They have perfect eyesight, and they jump out of the sand to catch their prey.

Other kinds of rays will be the best tank mates for motoro stingray. Although Cichlasoma severum, Geophagus, silver arowana and Polypterus species will also do as stingray tank mates.

Rays are one of the main predators in ecosystems where they dwell in the wild, and it’s not safe to keep them together with most of the other fish kinds in a tank. Their tank mates should be large enough not to become food for them, but peaceful enough as well not to bite rays or steal their food.

Thus, fish that swims in upper and medium water layers will be the best choice in this case. I’d advise avoiding armored catfishes as motoro rays tank mates, since there are a lot of documented reports saying that they get stuck to rays and damage their skin.

Gender differences: male vs female

Female species are larger than males, and they have two uteruses, which means that they can have offspring from two different males simultaneously. Males have modified fins that they use to fertilize the females.


Many aquarists succeeded in freshwater rays breeding, but this process takes time, you will need a large tank and dedication. Ocellate river stingray reproduces by ovoviviparity.

The motoro stingray female carries from 3 to 21 species, and they born completely ready to live on their own. The gestation period lasts from 9 to 12 weeks. An interesting fact is that this period is sufficiently shorter for rays that breed in tanks.

Possibly, due to the plentiful supply of food they have if compared to the fishes in the wild.

Rays may be quite picky when selecting their mate. So, just by buying a motoro stingray couple and putting them together in one tank, you won’t have any guarantee of successful breeding.

A perfect way of creating a fish couple is to get a group of juveniles, put them in a huge tank, and let them select their mates. However, this is quite a costly process, and most aquarists can’t afford it. Besides, it may take several years for the rays to become reproductive.

We should also mention that males of this kind are considered as the most furibund during the spawning period, and the females may not be ready for this.

If you keep a couple or a group of rays, be very attentive to their behavior during this period and be ready to separate them if necessary.