How do sharks control their buoyancy?
Since sharks lack a swim bladder, the organ that controls
buoyancy in bony fish, they have very large livers containing a
great deal of oil that helps them to stay buoyant. Most sharks also
generally stay in constant motion which, in addition to moving
water over their gill slits, also helps them stay buoyant through
the physical property of lift (similar to how airplanes stay in
flight by their wings) acting on their pectoral fins.