my book on freshwater stingrays talks about this for a while. mostly used by breeders and importers to protect themselves while treating the rays at their facilities before they are shipped out for sale. i think that most of them are removed before they are sold to their rightful owners, but i dont think it hurts the rays, more of a protection issue for people who work closely with them. i dont see many of them in home aquaria with the tubing still on, kinda tacky i think, but then again most owners are smart enough to avoid being stung in the first place, so the need for the tubing isnt necessary. hope i was of help
nitro