Swim bladders are gas-filled sacs found in many bony fishes. They help the fish maintain neutral buoyancy by adjusting the volume of gas inside. Blue whales, on the other hand, are mammals and have a different mechanism for maintaining buoyancy.
Instead of a swim bladder, blue whales have a thick layer of blubber, which is a layer of fat that helps them stay afloat and insulates them from the cold water. They also have a streamlined shape that reduces drag, allowing them to move efficiently through the water.