Sharks:
* Cartilaginous fish: Their skeletons are made of cartilage, not bone.
* Gill slits: They have five to seven gill slits on the sides of their heads.
* Scales: They have tough, sandpaper-like scales called dermal denticles.
* Teeth: Their teeth are constantly replaced throughout their lives.
* No swim bladder: They lack a swim bladder, so they rely on constant movement to stay afloat.
* Live birth: Most sharks give birth to live young, though some lay eggs.
* Predatory: They are mostly carnivorous, feeding on other fish, marine mammals, and invertebrates.
Fish:
* Bony fish: Their skeletons are made of bone.
* Gills: They have a single opening for gills covered by a flap called an operculum.
* Scales: They have bony scales that are usually smooth and overlapping.
* Teeth: Their teeth are usually fixed and don't continuously replace like shark teeth.
* Swim bladder: Most bony fish have a swim bladder that helps them control buoyancy.
* Lay eggs: Most bony fish reproduce by laying eggs.
* Diet varies: They can be carnivores, herbivores, omnivores, or filter feeders.
Here's a simple analogy: Imagine a shark as a super-advanced, streamlined sports car, while a fish is like a comfortable, versatile sedan. Both get you around, but they have different strengths and weaknesses.
To summarize, the key differences between sharks and fish are their skeletons, gills, scales, teeth, buoyancy mechanisms, and reproductive methods.