Freshwater stingrays are farmed and widely sold, but they remain very challenging fish to keep properly. The two main problems are their large size and their stiff requirements in terms of water quality. Anyone planning on keeping a stingray must carefully consider both of these issues beforehand. Even the smallest species will require a tank around 500 litres (110 Imperial gallons) in size, and because they need water with a very low nitrate content, a reverse-osmosis filter will probably be required to produce water of sufficient quality.
On the other hand, stingrays are fish of exceptional interest. They are often beautifully marked, and despite their size, they are essentially peaceful animals and easy to combine with a variety of tankmates. Given the right conditions they grow rapidly, and sexually mature specimens will breed fairly readily and the large ‘pups’ are relatively easy to rear. So while they are unquestionably difficult fish, it’s easy to understand why stingrays remain amongst the most popular oddballs in the trade.
Old World and New World species compared
Freshwater stingrays can be found in South America, Africa and Southeast Asia. The Southeast Asian and African species are members of the family Dasyatidae, a family that comprises over 70 species, most of which live in the sea. A few species in this family are adapted to freshwater conditions, while others are found in both freshwater and brackish water habitats. One of the most notable of the Dasyatidae is the Giant Freshwater Stingray (Himantura chaophraya) that gets to a disc width of up to 240 cm. Only occasionally are members of the Dasyatidae traded, and because some require brackish conditions for long term health, identification to species level is very important.
The South American freshwater stingrays belong to the family Potamotrygonidae, and are all completely adapted to freshwater conditions. So while there is some variation in terms of size and colouration, maintenance of all species is essentially similar. They are found across a wide swathe of the continent, from the Orinoco River in the southeast down to the River Plate. Several species are routinely traded, mostly Potamotrygon species rather than members of the two other genera in the family, Paratrygon and Plesiotrygon. In short, Potamotrygon spp. is by far the most commonly encountered freshwater stingrays and generally the easiest to keep.
Freshwater stingrays are all large, active fish. Because of their shape, they are more difficult to house than most other aquarium fish. A good rule of thumb is that the tank should be at least twice as wide as the disc width of the stingray being kept, and at least as long as five times the disc width.
For example, if a Reticulated Stingray (Potamotrygon orbygini) is being kept, it will need a tank at least 2 x 35 cm wide and 5 x 35 cm long, i.e., 70 cm wide and 175 cm long. If we assume the aquarium is as deep as it is wide, i.e., 70 cm deep, then its overall dimensions will be 175 cm long, 70 cm deep, and 70 cm wide. Such a tank has a volume of 857.5 litres, or just over 188 Imperial gallons.
It’s worth mentioning at this point that Reticulated Stingrays are among the smallest of the commonly traded species, and there are several species that get much bigger and consequently need even larger aquaria.
While juvenile specimens can be maintained in smaller aquaria, provided the proportions of the tank are as outlined above, stingrays grow quickly. By far the best approach is to buy the biggest aquarium you can right from the outset. Trying to keep a stingray in a tank that is too small for it is usually pointless because these fish become stressed very quickly. Suffice it to say that a stressed stingray quickly becomes a sick stingray, and these are not easy fish to medicate or otherwise treat.
Filtration, water quality and heating
Adequate filtration is critical to long term success. Without exception, stingrays are highly sensitive to ammonia and nitrite, and on no account should they be maintained in an immature aquarium. Filtration systems need to be robust and appropriate to the needs of large, carnivorous fish. Any heavy-duty filtration system might be used, but large external canister filters are generally favoured. Aim for water turnover rates at least 8 times the volume of the tank per hour, and ideally substantially above that.
Besides zero ammonia and nitrite levels, nitrate has to be kept as low as possible, preferably below 20 mg/l. Water changes are important, and these should be both regular and substantial, though water chemistry variation must be minimised. Because some tap water supplies contain high levels of nitrate, a reverse-osmosis filter may be required. As well as removing the nitrate, RO filters also remove other dissolved chemicals (such as hardness) from tap water. Before RO water can be used in the aquarium it will need to be hardened slightly with an appropriate mineral salt mix (as opposed to a chemical buffer that only fixes the pH). Commercial discus aquarium buffer salts are ideal, but otherwise a Rift Valley cichlid salt mix could be used instead, at a dose around 25% that required to harden water for a cichlid aquarium.
The use of a sump to increase water volume is highly recommended. Not only will this slow down any water quality problems, the sump can also be used to hold the heater. Stingrays are very prone to burns when kept in tanks with standard glass heaters. At the very least, use a heater that is protected with a heater guard. Stingrays are not fussy about water temperature, and between 25-28 degrees C suits the Orinoco and Amazon species well. River Plate species should be kept a little cooler, around 24 degrees C.
The South American stingrays come from water that is usually soft and slightly acidic. Ideal conditions would therefore be around 5-10 degrees dH, pH 6.5-7. In practice the water chemistry values aren’t critical, provided they’re stable. The most difficult stage is immediately after import, since wild-caught fish will have been collected from soft water conditions and it does take them some time to adjust to harder water. Tank-bred specimens are generally less troublesome, particularly if they’ve been bred in your local water conditions.
Water chemistry can be most easily kept stable through the use of RO water and a measured amount of mineral salt mix. Such mineral salt mixes include buffers that limit pH changes between water changes. If tap water is being used, it should be treated with a water conditioner that removes chlorine, chloramine, copper and ammonia. These are all present in some tap water supplies, and all are lethal to stingrays even at relatively low concentrations. Water changes should be regular, but not so large water chemistry changes significantly. It is best to do multiple small water changes (e.g., 10%) several times per week rather than one big water change (more than 25%) at the weekend.
Some stingray keepers maintain their fish in bare-bottomed tanks, arguing that this makes it much easier to keep the tank clean. Uneaten food and faeces are obvious and can be quickly removed (a turkey baster is ideal for spot cleaning). Other stingray keepers argue that smooth silica sand or fine gravel is a more natural substrate, and allows the stingray to dig itself in, just as it would do in the wild. Sand and gravel will also stop light from bouncing off the bottom pane of glass; this is helpful because upwelling light sometimes stresses fish. In practice both approaches work, and selecting one rather than the other is more a matter of personal choice than anything else.
Because stingrays like to dig in the sand, rocks and plants are more of a nuisance than a benefit. Use such decorative items carefully. Stingrays do not like bright light, and if live plants aren’t being used, then lighting should be minimal.
In the wild stingrays are opportunistic carnivores taking a variety of prey from insect larvae through to smaller fish. Recently purchased specimens prefer live foods, particularly earthworms and river shrimps, but once settled in, stingrays are adaptable and will feed on a variety of wet-frozen foods as well. As with any carnivore, care should be taken to minimise the use of thiaminase-rich foods such as prawns, mussels and squid. Foods that lack thiaminase include cockles, tilapia and pollack (coley).
Social behaviour and tankmates
Stingrays are not especially sociable, and they are most easily maintained singly. Males can be quite rough on one another, so if groups are to be maintained, it’s best to keep a single male alongside one or more females. Sexing stingrays is easy. Males have highly modified anal fins known as claspers that look a bit like fingers.
Because they are sensitive to poor water quality and easily damaged by nippy or aggressive tankmates, stingrays are best kept on their own. Tankmates can also cause problems at feeding time, and newly imported stingrays in particular are best kept in solitary until they’re feeding freely and clearly putting on weight. On the other hand, very small tankmates will be viewed as potential meals, even though stingrays are fairly inept piscivores. Medium to large barbs, rainbowfish, minnows and tetras have been kept with stingrays, but there are no guarantees that these won’t end up inside the belly of the stingray sooner or later.
The best companions are large but docile midwater fish. Oscars (Astronotus ocellatus) are particular favourites in this regard. Other good choices include Siamese Tigerfish (Coius spp.) Severums (Heros spp.) and Bichirs (Polypterus spp.) of similar size. Do note that small bichirs will be eaten, and unlike stingrays, bichirs will need a few caves and other hiding places dotted around the tank.
Suckermouth catfish are risky companions for stingrays. Several suckermouth cats have been reported rasping away at the bodies of stingrays, causing serious damage. This behaviour seems to reflect overcrowding and territorial aggression more than a parasitic feeding mode, which is why the combination of suckermouth catfish with a stingray should only be considered when very large aquaria are being used. Of course the suckermouth catfish should be large enough not be viewed as food, so rather than Ancistrus types catfish, the best choices would be species such as the Royal Plec (Panaque nigrolineatus).
Several Potamotrygon stingrays have been bred in captivity. They don’t seem especially difficult to breed, the main obstacles being those associated with simply maintaining a group of stingrays to sexual maturity. Sexually mature stingrays will be close to maximum size, and males start following the females about. If they can, they will bite the females and try to get them to mate.
Since stingrays mate belly-to-belly, and fertilisation is internal, the mating process is dramatic and distinctive. Given good conditions, mating happens quite readily. However, telling when females are pregnant isn’t easy. In theory at least, gestating females should become swollen somewhat, but this isn’t obvious in well fed specimens. Gestation period can be as long as six months, after which time up to eight pups are delivered.
Rearing the pups is much like maintaining the adults. They are fairly large when bought, around 10 cm in disc width, and while it takes about three days for them to use up the last of their yolk sac, once that’s happened they readily accept all sorts of small live foods (such as midge larvae and black worms). When they are eating well, they should be weaned onto wet-frozen foods.
Although adults are not aggressive towards newborn pups, it’s recommended the pups be moved to their own aquarium. This will ensure that they receive adequate food.
What to look for when shopping
It’s important to buy good quality specimens without any signs of physical damage. Healthy specimens should look fat, and if stingrays on sale in your shop appear ‘bony’, they’re best avoided. Ask to see the stingrays feeding: healthy fish are greedy, and it should be obvious if this is the case.
Avoid specimens exhibiting ‘death curl’, a syndrome where the edges of the disc curl upwards, like a bowl. This syndrome is caused by exposure to chronically poor conditions and generally precedes death. Recovery is uncommon, even if the stingray is moved to much better conditions.
Once purchased, the should be brought home quickly. Because stingrays are intolerant of changes in water chemistry, a drip method acclimation process will be essential. For the next couple of days there’s no point feeding the stingray, and it’s a good idea to leave the lights off so that the stingray can settle down into its new home.
Stingrays can all sting painfully, and should be handled with care. Normally the sting is used only when the animal is scared, and isn’t usually a problem. The South American stingrays have painful but not fatal stings; at least some of the Old World species have venom that is strong enough to kill. Anyone stung by a stingray should seek medical attention immediately, partly for pain relief, and partly to make sure none of the stinger is left in the wound, as this can lead to serious infections.
By far the most commonly traded freshwater stingrays are species from the South American genus Potamotrygon. Identification of particular specimens can be difficult because there are numerous lookalike species as well as several varieties that are traded but haven’t yet been scientifically described.
The Old World species of Dasyatis and Himantura are very rarely seen. Whereas the South American stingrays have circular bodies, the front of the Old World species is drawn into a distinctive triangular rostrum, almost like a nose. They also tend to have longer, more whip-like tails.
Amazon Stingray, Mottled Stingray (Potamotrygon hystrix)
This is a very widely sold species noted for its relatively small size (30 cm disc width) more than anything else. Compared to some of the other species, its pale brown mottling is not particularly striking.
Leopoldi Stingray, White-blotched Stingray (Potamotrygon leopoldi)
This is one of the less often seen species. It has a dark body with off-white circular blotches, and gets to a disc width of up to 60 cm. Given its very large size, this is a very challenging species to maintain at home.
Motoro Stingray (Potamotrygon motoro)
This is a relatively large species, with a disc width of up to 50 cm. It is very pretty though, with circular markings dotted across the body. Despite its large size, this species is quite widely sold. There are numerous varieties, each differing slightly in colouration and markings.
Reticulated Stingray (Potamotrygon orbignyi)
Another very commonly traded species that occurs in several colour forms, one of which was formerly known as Potamotrygon reticulata, hence the common name. Disc width is around 35 cm.
Teacup Stingray (Potamotrygon spp.)
A ‘teacup stingray’ is merely a juvenile Potamotrygon of some sort, typically one of the species mentioned above. It isn’t a unique, dwarf species of stingray, and kept properly will get much larger.
Bleeker’s Whipray (Himantura bleekeri)
A typical brackish water stingray, this species is occasionally traded as a freshwater fish. It cannot be maintained as a freshwater fish indefinitely, and should be kept in at least moderately brackish conditions, around SG 1.010. Maximum disc width is around 100 cm, so while juveniles might be sold to hobbyists, this is really a species for the public aquarium only.
Marbled Freshwater Whipray (Himantura signifer)
This Southeast Asian species has some aquarium potential, reaching only 40 cm in disc width and sporting attractive markings on the disc. It is found in both fresh and brackish water habitats. Whether it can be maintained permanently in freshwater conditions is unknown.