What is a fin?

What is a fin?

• A. A limb used for digestion.
• B. A limb used by fish for movement and stability in the water.
• C. A brain region controlling swimming.
• D. A protective shell around the body.

Answer: (B)

Fins are external appendages that fish use to move through water and stay stable. They act like paddles and fins on a boat: the tail (caudal fin) provides forward thrust, while dorsal, pectoral, pelvic, and anal fins help with steering, stabilization, and braking. This combination lets a fish swim, hover, and maneuver in currents. The other options miss the function: digestion happens in internal organs, not limbs; a brain region would govern movement rather than be a limb itself; and a protective shell is a different structure, not a fin.