An air sac, sometimes double or variously lobed, in the visceral cavity of many fishes. It originates in the same way as the lungs of air-breathing vertebrates, and in the adult may retain a tubular connection with the pharynx or esophagus.

A sac or bladder full of air in an animal or plant; also an air hole in a casting.

a gas filled bladder in many teleost fish, serves as hydrostatic organ.

Part of an algae which traps an air bubble used in raising the algae into the water column.