FAR below the clear blue surface of the sea is a world full of strange, ferocious-looking creatures.
Sea exploration has been made easier by new technological developments, but countless mysteries remain, waiting to be solved by the scientists of the future.
Many of the deep sea fish have lights on their bodies. These serve to attract prey, as in anglerfish which have luminous rods attached to the head, or mates (it is difficult finding one's true love in the dark!) or to confuse predators (certain crustaceans spill out clouds of light while trying to escape).
The greatest depth at which fish are known to live is at 7,965 metres in the Puerto Rico Trench in the Caribbean Sea - that is nearly as deep as Mount Everest is tall. The fishes are therefore adapted to intense cold and die when they are brought to the warm surface.
Deep sea fish have huge eyes so as to enjoy maximum vision. Others are blind and possess different senses to enable them to find their way.
Think of the underwater world as an inverted mountain. Just as on dry land great height brings a shortage of oxygen, a decrease in pressure and cooler temperatures, so great depths bring the same. The only difference is that on the ocean bed the pressureincreases.