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Fact Sheets for "Sharks" 
both True Sharks and fish
referred to as Sharks
 
 
 
 
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Sharks

The true sharks are mostly large marine fish with a skeleton made of cartilage rather than bone.  Although these fish are predominately salt water fish, some species do penetrate into fresh water.  In particular, the Bull Shark has been recorded as far inland as Saint Louis in Missouri.   The Bull Shark will occasionally attack people.  The Great White Shark has also been known to attack Humans. 

The largest of the sharks alive today is the Whale Shark, and the second largest is the basking shark.  These giants of the sea are plankton feeders and do not attack people or other large creatures.

Sharks do not have a swim bladder, but have reserves of oil in their livers that help to make them buoyant.  Many types of shark cannot breathe effectively unless they are moving through the water.  These sharks rely on their movement relative to the water to create a current over their gills.  Some sharks have developed ways round this problem so they can stay in one place, often on the bottom of shallow seas.
 
Many sharks have live young while others lay eggs like the one in the picture on the right.

Apart from the true sharks there are many fish referred to as sharks by aquarists.  The Black Shark can reach four feet long in the wild.  The Redtail Black Shark is another rather aggressively territorial aquarium shark.

Perhaps the most shark like in appearance, but the least shark like in behaviour is the Silver Shark.

The Scissortail Shark is another name for the Scissortail Rasbora.