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Sharks Information With Pictures
 Sharks There are many different types of shark .Sharks, together with rays and skates, are different from other fish. Their skeleton is made entirely of cartilage rather than bone. Their skin is made of thousand of tooth-like structures known as ‘placoid scales’. They give shark akin a texture like sandpaper. The teeth in a shark’s jaws are modified placoid scales and grow in rows. When a tooth is damaged it drops out and the next tooth behind moves forward to replace it. At any one time the shark may have up to 3,000 teeth in its mouth. The teeth may be pointed and serrated for sawing flesh or flattened for crushing shellfish. Another way in which sharks differ from most other fish is that they do not have a swim bladder, a gas-filled organ, to keep them afloat. If they stop swimming they sink. Sharks produce very few eggs, and unusually for a fish, the eggs are not released, but fertilized within the female’s body. In most shark species the eggs hatch within the female and she gives birth to live young. However, in some species, the eggs are protected by horny egg cases. The ‘mermaid’s purse’ you may find on the seashore is the egg case of a shark, the dogfish. Sharks have a keen sense of smell and can detect one part of blood in a million parts of water. They also sense vibrations produced by struggling fish. Shark fishermen in the pacific islands rattle coconut shells under-water to attract them. All sharks can detect electricity through a series of pits in their snout. This means they can detect the electrical charge produced by the nerves in an animal’s body. Sharks are also able to see very well in dim light. A completely new species of shark over 4.5 m (15 ft) long was also described in 1983. It has been named the mega mouth shark because of its huge mouth. It is a filter-feeder like the whale shark and eats shrimps and jellyfish. So far only three specimens have been caught. There are fewer than 100 shark attacks upon humans every year. However, thou-sands of sharks are killed for food and liver oil. The ‘rock salmon’ used in fish and chip shops is a shark, the lesser spotted dogfish. |
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