Scientific classification: Sharks belong to the class Chondrichthyes and the subclass Elasmobranchii. The estimated 375 species are divided into 8 orders and 30 families.
Sharkare generally large fish known for their many sharp teeth, distinctive dorsal fin, and skill in locating underwater prey. Like other fishes, sharks are generally cold-blooded and breathe with gills. But unlike the more common bony fishes, shark facts for kids which have skeletons made of rigid bone, sharks and their relatives skates, rays, and chimaeras have flexible internal skeletons made of cartilage.
Sharks have streamlined bodies that permit short bursts of movement through the water at high speeds. Their long bodies taper into a blunt or slightly pointed snout on one end and a powerful tail fin on the other. This shape reduces drag in the water, enabling sharks to glide gracefully, expending minimal energy as they swim. Generally, sharks swim at speeds less than 5 km/h (3 mph), shark facts for kids but many can reach speeds of more than 20 km/h (12 mph) in short bursts. Mako sharks, swift, powerful, open-ocean sharks that reach lengths of up to 3.5 m (12 ft), are believed capable of speeds up to 48 km/h (30 mph).
Although some sharks grow to more than 15 m (50 ft) in length, massive size in sharks is the exception rather than the rule. About half of all known species never grow to more than 1 m (3 ft) in length, and less than 20 percent reach lengths longer than 2 m (6 ft). Some of the best-known sharks, however, are the largest sharks. Nurse sharks, slow-moving sharks that live mostly in warm, shallow water, grow to more than 4 m (13 ft). Hammerheads, tropical water sharks known for their flattened, T-shaped heads, shark facts for kids frequently exceed 3.5 m (12 ft), and great white sharks, perhaps the greatest predators of the sea, often reach lengths over 6 m (20 ft).
Reproduction and development
Mating behavior in sharks is complex, and very few people have observed it in detail. Biologists know that female sharks mate for only a few weeks during the mating season, which occurs once a year in some species but only once every two or three years in other species. Unlike other fishes, which may produce thousands of offspring each time they reproduce, shark facts for kids sharks generally do not reproduce in large numbers. Some species may produce only one baby, or pup, at a time, while others may produce 20 or more.
Research and Conservation
Humans have hunted sharks for sport, food, medicine, and leather for centuries, with little regard for the health of shark populations. Sports fishers around the world regard sharks as some of the most challenging fish to catch in the sea. Shark flesh is highly prized in many regions of the world. One particularly popular food made from shark meat, shark fin soup, is in such demand that some fishers hunt sharks just for their fins, throwing the rest of the fish back to the sea to die. Shark liver oil is a popular source of vitamin A, and some people believe that shark liver and cartilage are beneficial to human health. Shark skin, with its microscopic teethlike scales, was once used as a fine grade of sandpaper, and when the scales are removed from the skin to make shark leather, shark facts for kids it brings high prices for use in shoes, belts, and handbags. Many sharks are killed unintentionally. Each year, thousands of sharks die in nets set out to catch other types of fish. Sometimes, humans kill sharks just because they fear them.