Image (c) Picture Is Unrelated
A budgerigar, submerged in water, breathes through a transparent silicone rubber "gill". Through bionic research, people aided by such gills may someday breathe underwater. The budgie sure looks fascinated by the fish, but the picture is probably a fake. Budgies are airborne creatures and cannot swim, so a swim tank would be the least suitable place for them. Please keep that in mind when you let them fly around in the house, in order to avoid accidents. Would be cool though, if somehow they found a way to make all animals and humans breathe underwater. Can you imagine a budgie exploring the vast oceans of the world?
Thanks to my fiancé for finding this picture! :)