As submarines go deeper they are surrounded by more and more pressure from the water arround them. There are not currently any submarines that can withstand that amount of water pressure.
Submarines cannot reach the deepest parts of water because of the pressure or water and deepest surface is not a smooth, its full of rocks and sea plants.
Humans have problems diving to extreme depth. SCUBA by definition is self contained and cannot get close to the life support potential of submarines. Specialist submarines like the bathyscaphe can reach the deepest parts of our oceans.
bathyscaphe
The Pacific Ocean has the deepest trenches.
with a submarine or a machine called "Alvin"
Piranhas live in freshwater rivers not in oceans at any depth.
The Marianas Trench is the deepest point of all the oceans and is located in the pacific ocean. The deepest parts of the ocean get no sunlight at all because they are so deep. This is known as the midnight zone.
The Earth's outermost layer, the lithosphere, contains the highest mountains such as Mount Everest. The deepest parts of the ocean, including the Mariana Trench, are found in the Earth's oceanic crust, which is part of the lithosphere that lies beneath the oceans.
The deepest parts of oceans are dark all the time because natural light does not penetrate to the ocean depths. Little is known about life in the depths of the ocean. More is known about the moon than the depths of the oceans. Water pressure is great, the temperature is constant.
Middle parts
They live of by eating other animals of their own type and maybe they have a great ability of not getting hungry.
The deepest parts of the ocean floor are caused by plate tectonic subduction and occur where the sea floor sinks back into the mantle in a subduction zone. These areas are called deep sea trenches and the Challenger Deep in the Mariana Trench in the Pacific is the deepest known point in Earth's oceans.