Which of the following is NOT shared by all fishes?

You're asking a great question! Here's the breakdown of why the answer is lungs:

* Fins: All fish use fins for movement and stability in the water.

* Scales: Most fish have scales for protection, though some have evolved to have different coverings like bony plates.

* Gills: This is the key to aquatic respiration. Gills extract oxygen from water.

* Lungs: While some fish have evolved lungs (like lungfish), this is not a universal characteristic of all fish.

Let me know if you'd like to know more about fish biology!