|1.||ichthyol Also called: swim bladder an air-filled sac, lying above the alimentary canal in bony fishes, that regulates buoyancy at different depths by a variation in the pressure of the air|
|2.||any air-filled sac, such as one of the bladders of seaweeds|
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)
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