Care
The Motoro Stingray has a wide area of distribution, through much of the Amazon basin and numerous smaller rivers including the Rio Orinoco, Rio Paraguay, Rio Paraná, and Rio Uruguay. Here, it is found in a variety of habitats, but most commonly encountered in shallow, slow-moving tributaries over sandy or muddy substrates. This beautiful bottom-dweller grows very large, and requires a voluminous aquarium with powerful filtration to match. The length and width of the tank is generally much more important than the height, giving this fish as much floor space as possible and allowing for the fish to turn freely with the long tail. The aquarium must be biologically mature before adding this species. A soft sand substrate is essential, as stingrays spend the majority of their time on the bottom and like to bury themselves in the substrate from time to time (with just the eyes protruding), as well as searching out food items on the sand. When resting on or in the substrate, small openings located on the top of the head (known as spiracles) draw water into the gill chambers to facilitate oxygen exchange. Decor is not overly necessary for stingrays, as a large expanse of sand is much more important for their continued wellbeing. Some tangles of driftwood and smooth rocks could be incorporated, but these must be very secure, and not take up very much of the floor space. The Motoro Stingray is a voracious eater that produces a lot of waste, and requires continuous excellent water conditions. To this end, filtration must be powerful and the water well-oxygenated. A frequent partial water change regime is absolutely essential as this fish will not tolerate an elevated nitrate level. Several huge canister filters can be employed, but sump filtration may be more prudent as then equipment such as heaters can be kept in the sump and out of the main tank where they would be very easily damaged. Lighting should be fairly dim, as these fish do not enjoy bright illumination. Stingrays are not particularly sociable and are best maintained either singly, as a male/female pair, or one male with a group of females. Male fish can be rather rough with one another, so it's best to house only one male per tank. Tankmates (if desired) must be chosen very carefully, as stingrays are highly proficient predators; however, despite this, they will fail to thrive if housed with boisterous or territorial species. The best companions would be large, passive midwater or surface-dwelling fish. Avoid keeping with Loricariids (suckermouth catfish) as within the confines of the home aquarium, there are many documented instances of them attaching themselves and rasping away at the flat, disc-shaped body of stingrays, causing injury. Ensure the tank has tight fitting coverslides that are weighted down, as these fish are expert jumpers. Take extra care when offering food, as it is not unusual for the stingray to swim up and breach the water's surface during all the excitement of a feeding frenzy. Like all species from this genus, P. motoro is equipped with one or more barbed spines that are found on the dorsal surface of the middle section of the tail. These spines are coated with an extremely toxic mucus that inflicts very painful wounds, and tends to be employed in defence or when the fish is alarmed. Always handle stingrays with much care. When these fish need to be moved, they should always be herded into a solid container, rather than using a net. If you are stung by a Potamotrygon spp. stingray, seek immediate medical help for pain relief and to ensure no part of the stinger remains in the wound (this could lead to a serious secondary infection). These fish shed their stingers every 2-3 months and new ones grow in their place. Be aware that discarded stingers can remain venomous for some time, so exercise caution when carrying out tank maintenance. This fish is long-lived (20+ years) and a fascinating species to look after, but it is quite the commitment so do ensure that all of its specific care requirements can be met before purchase. May also be seen on sale as the Ocellate River Stingray or the South American Freshwater Stingray.
Feeding
Juveniles can be offered bloodworm, vitamin-enriched brineshrimp, Mysis shrimp, and chopped krill. Adults should be offered larger foodstuffs such as cockles, mussels, prawns, river shrimp, silversides, whitebait, and pieces of white fish flesh. Stingrays have a fast metabolism and require feeding 2-3 times per day (which is why powerful filtration and a strict water change regime is absolutely essential).
Breeding
The Motoro Stingray has been bred in the home aquarium, and like other Potamotrygon spp. reproduces via a breeding strategy known as matrotrophic viviparity. Stingrays take many years to become sexually mature, so patience may be required, particularly if starting out with fairly young fish. As the courtship ritual can be a somewhat violent affair, it is essential that the female is larger than the male so that she can defend herself adequately from the male's advances, which includes incessant chasing and rough biting. Always observe carefully just in case the female is not receptive, as the fish may need separating for safety reasons. When ready to spawn, the pair briefly go belly-to-belly, with the male inserting one of his claspers into the female's cloaca, fertilisation taking place internally. Gestation usually lasts 2-3 months, and a typical sized litter would number between 1 and 8 (the young often referred to as 'pups'). The pups develop inside the mother, nourished by secretions from her villi (umbilical filaments), and when they are born, they are fully-formed miniatures of the adults. It is essential that the female receives good, nutritious feedings during the gestation period as she will expend a lot of energy when carrying and nourishing her pups. Once the pups are born, it may be best to move them carefully to other quarters, as although predation is rare, it is not unheard of. There is also the matter of the water becoming very clouded during the birth when bodily fluids are released, so the main tank will require a large water change (which the pups might be sensitive to). The pups will feed from their yolk sacs for the first week or so, after which time they can be offered a variety of small meaty frozen foods. A compatible pair of stingrays may attempt to breed regularly, and as this can be rather hard on the female, it may be best to separate the pair after every couple of litters, in order for her to recover properly and have a rest from such an energy-intensive process.
