BIO325H5 Lecture Notes - Lecture 3: Swim Bladder, Siphuncle, Neutral Buoyancy
Document Summary
Swim bladder /gas bladder, many bony fishes have a single median gas chamber (developing as a diverticulum of the gut) used to change their density; it gives neutral buoyancy at different depths in the water column. When some of these ancestors reinvaded the seas these lungs evolved into swim bladders. Chamber water replaced by gas: a growing nautilus,vacating a chamber, slowly replaces the chamber seawater with gas, changing its body (+ shell) density. Oxygen, and carbon dioxide, diffuse out of the siphuncle blood into the emptying chamber: replacing water with gas reduces shell density and changes the nautilus" buoyancy. The regulation of buoyancy in this way is apparently a relatively slow process compared to depth regulation by fish swim. The high bulk modulus of the water means it is incompressible and so it is displaced, accelerated out of the hyponome*, an action force that evokes a reaction force called thrust.
