Swim bladders and lungs are similar organs, although they are used for different things and found in different groups of fish. They both develop from a location in the upper throat called the pharynx, they both are used to manipulate gases, and they both have a good blood supply. However, the lung is used for breathing, and, besides being found in land vertebrates, is also found in a few groups of fish like lungfish, which likely were the ancestors of land vertebrates.
The swim bladder, on the other hand, is used to control buoyancy, and it is found in all other bony fishes. It is basically an inflatable bag. Fish use the swim bladder to control their buoyancy by filling it with oxygen from their gills using a gland called a gas gland. This increases the volume of the bladder and pushes the fish toward the surface of the water.
Strangely, some fish also use their swim bladders to breathe. These fish live in muddy waters that are low in oxygen, and they have a tube that runs from the swim bladder to the gut, so that when they gulp air from the surface they can push the gas into the swim bladder.
Darwin believed that lungs evolved from gas bladders, but the fact that fish with lungs are the oldest type of bony fish, plus molecular and developmental evidence, points to the reverse — that lungs evolved before swim bladders. Gills were present in the earliest fish, but lungs also evolved pretty early on, potentially from the tissue sac that surrounds the gills.
Chute sent a letter to the director of the aquarium at Sydney's Taronga Zoo and his crew returned home in with not one, but two lungfish : Granddad and his mate, who lived until These days, Granddad spends most of his time doing his best imitation of a fallen log. He breathes both underwater and from the surface, and has been known to startle his caretaker with loud snorts when he comes up for air. A rare species Throughout the world, there are only 6 species of lungfish—one in South America, one in Australia and four in Africa.
The Australian or Queensland lungfish is the most primitive out of the bunch with only a single lung, compared to the paired lungs the others have.
Being able to breathe air makes Granddad particularly fascinating because of the advantage it gives him out in the wild: surviving droughts and surviving in general. Most fish will dig mud pits or retreat to crowded pools of water to survive when harsh heat causes rivers to dry up in tropical climates. This is problematic as fish get crowded together.
If you've ever been in a room that is packed to the gills pun not intended , you'll know that things can get uncomfortable fast—it gets hot and the air gets really stuffy. Same goes for this large pool of evaporating water. With more fish using up the remaining oxygen in the shrinking pool of water, the less oxygen is available underwater for the fish to breathe. Here's where lungfish have an advantage.
Unlike other fish with gills alone, lungfish can surface, take a breath and survive when other fish might be lacking air. In fact, much like many sea mammals, lungfish are obligate air breathers—they have to breathe air above water periodically to survive. Granddad the lungfish, who was known to be the world's oldest living aquarium fish , lived to be about years old. He spent the last 82 years of his life at Chicago's Shedd Aquarium.
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