Depending on the species freshwater rays grow to anything from 15" to 30" in diameter, females are generally larger than males.
They require far more care than any normal tropical fish and should only be kept by competent and experienced fishkeepers, ideally some experience with other sensative fish like discus would be recomended. They do not tolerate nitrogen pollution at all so require a well matured and stable tank, ammonia and nitrite shouldnt even be talked about where rays are concerned, the smallest of spikes will probably result in a dead ray. Nitrate should always be below 20ppm, if your tapwater cant supply this then you will need to invest in a RO machine. The pH can be as high as 7.5 but it is best to try and match the water the lfs has been keeping the ray in, rays do not tolerate changes well.
They are known for being incredibly fussy eaters, if possible for a first ray try and buy one that is already feeding well on frozen meaty foods. If the ray you purchase is not eating then you may have to offer live foods to keep it alive until you can ween it onto frozen, this will mean weeks of supplying large quantities of live bloodworms and shrimps every day, feeder fish are not recomended due to the risk of disease.
The best set up for rays would be a long wide shallow tank with a minimum footprint of 60x24", height isnt really important and can be as shallow as 15". A sand substrate is a must and the bottom should be as clear as possible to provide maximum swimming area. They can be kept with tankmates but you will need to keep them to a minimum to keep the nitrates down, large peaceful cichlids like severums or discus, bichirs and non aggressive surface dwellers like arowanas all make good tankmates, bottom dwellers and any fish with reputation for fin nipping should be avoided.
