Freshwater Stingrays
by Chris Guarino

Definitely one of the most interesting fish available for freshwater tanks, Freshwater Stingrays of the genus Potamotrygon come from South American waterways and provide an unusual addition to any collection. Unfortunately, there are a few major characteristics that make this fish less than ideal. The first and foremost is their size. Stingrays can reach up to 14" in the aquarium, and as much as 30" in the wild. Another is the lack of time this fish has been in the hobby. Being a fairly new addition to the hobby, stingrays can be relatively hard to acquire, and usually carry a hefty price tag (from $75 to over $200, depending on size and species). The most obvious reason a stingray is not for a novice is the barbed sting located just behind the base of the stingray’s tail. In some cases, stings can be excruciating but there are seldom serious consequences. They are not aggressive, however, and captive specimens are not likely to attempt to sting, but care should still be taken to avoid the spine.

Despite the many flaws in the freshwater stingray, there are many more attributes. Stingrays are totally non-aggressive towards other stingrays, and can be kept in large groups without the fear of fighting or subordination. Stingrays are, however, totally aggressive towards any thing that they consider food, which includes the standard bloodworms and tubifex, but also earthworms, frozen shrimp, small or prepared fish, and anything else that can fit into a stingray’s mouth. This unfortunately makes stingrays bad candidates for the community aquarium, leaving only larger and more robust species as suggested tank mates. Surprisingly, a plecostomus should not be added to a stingray community, as they have a tendency to suck on large and flat fish. This can be not only irritating to the stingray, but also damaging, as it disturbs the slime coat that surrounds the stingray’s body.

Stingrays also have little discrimination against water parameters, they enjoy a wide range of temperatures, from 72-88 and have been spawned in water with a ph of 8.2 and a hardness of over 250 ppm, despite the fact that they come from the soft, acidic waters of South America. Frequent water changes are a must, however, and should constitute a 20-40% change about twice a week.

These fish also are incredibly easy to sex. Males have long claspers underneath their tails, while females lack these fins totally. Stingrays also give birth to live young, having one or two at a time. These young are perfect miniatures of their parents, and can be cared for as such. Courtship consists of the male chasing and nipping the female, and pregnant females are easily distinguished by the large humps that appear on either side of the spine and towards the back of the disk.

Stingray aquariums are best when long and broad, as height is not very important to these bottom-dwelling fish. An adequate filtration system is a must, and spillway filtration systems are optimal. Spillway systems consist of a closed off corner of the tank, from which water is pumped through filtration equipment and then back into another part of the tank. Heaters are also a must, but need to be kept covered to prevent the serious burns that the stingrays’ sensitive disks are prone to. Substrate is best kept to sand or a bare bottomed tank. Sand provides hiding for stingrays, as they will bury themselves for protection, but is harder to clean, whereas bare-bottomed tanks are very easy to clean, but leave rays feeling vulnerable. Rays may also prefer sand due to the fact that they will "walk" along the bottom with the fins under their disk, and bare tanks provide less traction.

There are also many different varieties of stingrays. They can be black with white or yellow spots, reticulated brown and black, black with large brown blotches, plain beige or brown, or with yellow and black markings. Most species of ray have large eyes that rise from the top of the head and face outwards, while other rays, such as china rays, have flat eyes that face upwards.

Stingrays may suffer from various ailments; the most severe of which is fin curl. Fin curl is the progressive curling up of the disc, and is almost always fatal. Specimens with fin curl usually contract the problem from prolonged stress, and specimens with fin curl should be avoided at all costs. Rays may also contract fish lice, especially rays that are wild caught. Fish lice are flat parasites that stick to the ray and should be treated with manual removal, as they are 2-3 mm in diameter and fairly easy to eradicate in small numbers. Other diseases are best treated via injection of antibiotics, which should be observed before attempted.

Despite the flaws in the Freshwater Stingray, they provide a unique fish for the experienced aquarist who can afford the fish, the room, and the time to care for them properly. Rays that are cared for well will reward their owners with robust behavior, insatiable appetites, and maybe even a baby or two.