| 1. | a vesicle or sac containing air. |
| 2. | Also called gas bladder, swim bladder. Ichthyology. a gas-filled sac located against the roof of the body cavity of most bony fishes, originally functioning only as a lung, now serving in many higher fishes to regulate hydrostatic pressure. |
| air bladder n.
|
| swim bladder n. See air bladder. |
air bladder
|
swim bladder  (swĭm) Pronunciation Key
See air bladder. |
swim bladder
buoyancy organ possessed by most bony fish. The swim bladder is located in the body cavity and is derived from an outpocketing of the digestive tube. It contains gas (usually oxygen) and functions as a hydrostatic, or ballast, organ, enabling the fish to maintain its depth without floating upward or sinking. It also serves as a resonating chamber to produce sound. In some species the swim bladder contains oil instead of gas. In certain primitive fish it functions as a lung or respiratory aid instead of a hydrostatic organ. The swim bladder is missing in some bottom-dwelling and deep-sea bony fish (teleosts) and in all cartilaginous fish (sharks, skates, and rays)
Learn more about swim bladder with a free trial on Britannica.com.