By Douglas Whitbread Stunned staff at an aquarium believe that their lone female stingray may have been impregnated – by a shark. Charlotte, who lives at the Aquarium and Shark Lab by Team ECCO , in North Carolina, was originally thought to have cancer after keepers noticed a lump on her back. But following further examination using ultrasound equipment, it was revealed that the swelling was actually a sack of eggs that were close to hatching. As there were no male stingrays in her tank, baffled staff considered the possibility that she may have been impregnated by one of their whitespotted ba…