The air bladder (or swim bladder) is a special organ found in bony fishes (Osteichthyes).

Importance

• Buoyancy control: helps the fish float and move to different water levels without wasting energy.
• Balance & stability: keeps the body steady while swimming.
• Respiration: in some fishes, it also helps in gaseous exchange and breathing.

Without it, fishes would sink and need to keep swimming continuously to stay afloat.