ATLANTA - The world's largest aquarium is expecting the pitter patter of giant fins.

The Georgia Aquarium has a rare beluga whale pregnancy, the first mammal to conceive at the downtown Atlanta attraction since it opened in 2005. And the proud mom, Maris, conceived naturally, which is rare for belugas in captivity.

Maris is being monitored round-the-clock as she gets closer to the end of her 14-month pregnancy. She is expected to give birth by June to a calf that could be up to 50 pounds.

Just six North American facilities house belugas and few are born each year. Newborn calves often don't survive with first-time mothers, but aquarium officials are working to train Maris on how to nurse and care for the baby.