A dolphin has had her pregnancy confirmed after she underwent an ultrasound scan at a US zoo.Tapeko, a common bottlenose dolphin, was given the examination at Brookfield Zoo in Illinois.The 29-year-old dolphin was happy to float belly-up for the check up - in exchange for a fish reward.Veterinary staff confirmed the pregnancy during the ultrasound and will continue to monitor the development of the fetus, which has a 12-month gestation period.Tapeko already has two daughters, Noelani, seven, and five-year-old Allison, 5, who live with her at the zoo.She was also surrogate to her grandson when one of her daughters could not provide the proper care for her own calf. Chinook, 28, is the father of the calf due in the autumn.Zoo spokeswoman Sondra Katzen said: "Due to the relationship built on mutual trust and respect between trainers and animals, Tapeko voluntarily cooperated during these exams, allowing the veterinary staff to administer the ultrasound."She is rewarded for this behaviour with food or a favourite toy."Source: orange.com