The first amphibians used the scaly exterior of the fish to prevent drying out of the body surface. You might ask about frogs at this point. Modern day frogs do not have scales and have a thin skin which is subject to drying. Salamanders and frogs evolved from early amphibians by reducing size, losing their scales, and relying on respiration across their skin to supplement their lungs. Another interesting problem is that of hearing.
Sound passes easily from water into tissue.
So, fish don't need a very complicated system to hear underwater. Their hair cells , specialized receptor cells of the nervous system, are arranged along the side of the fish in a structure called the lateral line . This is the principal sensor of sound and vibration in fish. The lateral line and similar types of structures don't work well in air because the transfer of sound from air to solid or water isn't very efficient. And, upper part of the hyoid arch , a bony jaw brace in early fishes, became the stapes , located in a new part of the ear, the middle ear.