.
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 gill. 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.
Sharks
