Final answer:
Sharks do not have gills and scales like trouts. Trouts have specialized gills for breathing underwater and scales for protection and streamlined movement.
Step-by-step explanation:
Sharks do not have gills like trouts. Instead, sharks have to constantly move in order to force water over their gills to extract oxygen. Trouts, on the other hand, have specialized gills that allow them to extract oxygen from water.
Both trouts and sharks have cartilage as their skeleton, but trouts also have scales, which sharks lack. These scales provide protection and help streamline the fish's body for efficient swimming.