Sharks are a type of fish.

ATTRIBUTE	SHARKS	BONY FISH
Skeleton	Cartilage only	Bones and cartilage
Swimming	Can only swim forward.	Can swim forwards and backwards
Buoyancy (floating)	Large oily liver	Gas-filled swim bladder
Gills	Gill slits but no gill cover	Covered gill slits
Reproduction	Eggs fertilized in female's body.	Eggs usually fertilized in the water.
Skin	Rough, sandpaper-like placoid scales	Slippery, overlapping scales

SIZE

A scuba diver above a Whale shark. The Whale shark is the largest fish in the world; the basking shark is the second largest fish.

There are many different species of sharks that range in size from the size of a person's hand to bigger than a bus. Fully-grown sharks range in size from 7 inches (18 cm) long (the Spined Pygmy shark), up to 50 feet (15 m) long (the Whale shark). Most sharks are intermediate in size, and are about the same size as people, 5-7 feet (1.5-2.1 m) long. Half of the 368 shark species are under 39 inches (1 m) long.

There are about 368 different species of sharks, which are divided into 30 families. These different families of sharks are very different in the way they look, live, and eat. They have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes. Some types of shark are very rare (like the great white shark and the megamouth) and some are quite common (like the dogfish shark and bull shark). Sharks belong to the group of cartilagenous fish, the Elasmobranchii, that includes the sharks, rays, and skates.

There are over 350 different species of sharks. The spiny dogfish shark is the most common shark.

Sharks (like the Goblin Shark pictured above) have no bones; their skeleton is made of cartilage.

• Some (like the great white, mako, tiger, and hammerhead) are swift predators that eat fish, squid, other sharks, and marine mammals.
• Some (like the zebra horn shark, angelshark, and wobbegong) are slow-swimming predators that crush and eat shellfish (crabs and clams) from the ocean floor.
• Others (like the whale shark, the basking shark, and the megamouth) are filter feeders that sieve tiny bits of plankton and small animals from the water as they swim with open mouths. They eat huge amounts of these tiny animals and plants.

bull shark

• Local sharks - these sharks do not migrate, and range only about a hundred miles from their habitat. Examples include the bonnethead shark, and the nurse shark.
• Coastal pelagic sharks - these sharks can migrate over 1,000 miles (1,600 km). Examples include the dusky shark, the blacktip sharks, the tiger shark, and the sandbar shark.
• Highly pelagic sharks - these sharks migrate across oceans. Examples include the blue shark and the mako.

For more information on early sharks, click here.

The Basking shark, a species in decline.