Centralized nervous system with the addition of lay lines, gills are effectively identical, body lay out between sharks and fish of the same size and habits are similar, although the fish of that size (such as some pike, when compared to smaller sharks) are significantly more streamlined as they are less flexible.
The most defining factor between fish and sharks are that sharks have no bones! They are made up of cartlidge. In addition sharks have no gill flaps that can move water over the gills to provide oxygen to them..so that is why a shark has to keep moving all the time. If you ever looked at a fish (like a goldfish) you can see they move their gill flaps to move water over the gills. Sharks don't have that and If they didn't keep moving..they would suffocate. There are a a lot more then that but that is the basic jist of differences between boney fish and cartilaginous vertebrates.