Depends on the Species.
Blue-spotted ribbontail ray (Taeniura lymma) grows to a total length of 27.5"
Blue-spotted Stingray (Dasyatis kuhlii) grows to a total length of 26"
The Blue-spotted Stingray is the hardier species. The Blue-spotted ribbontail has a very low survival rate.
For Blue-spotted rays remember the following - Diamond good, round bad. The Blue-spotted Stingray has a diamond shaped disc, while the Blue-spotted ribbontail has a round shaped disc.