Body structure

A solar light hardly reaches deep sea.
Moreover, water pressure is high, the temperature of water is also low, and there are few organic matters which can be used. Thus, conditions with deep sea severe for a living thing are met. In order to live in such environment, deep sea fish fish has the various unusual features in the body. It is considered that the device would like to introduce this time. The bone and muscles in the body of fishes are heavy. The fish which lives in a shoal has acquired lift by swimming. In scarce deep sea, the deep sea fish needs to secure lift to the energy which can be exploited, without swimming as much as possible. In many deep sea fish fish, tissues in the living body, such as a bone, a cartilage, and muscles, are decreasing in number. Instead, moisture and fat are included so much.
A small kind and a kind without a scale also have many frames of a head, and they are estimated at one means towards a weight saving. A bladder is a general means by which the fish which lives in a shoal acquires lift. However, since water pressure is very high, it is not expectable in the function of a bladder in deep sea.
In order to be equal to flood pressure and a rapid pressure change, deep sea fish's wall of a bladder is thick, or the device of transposing a content to not gas but fat or wax is seen.
Sunlight arrives barely to about depth-sounding 1000m.
Therefore, what has a very big eyeball in the deep sea fish which lives in this domain to the body is. The light which arrives at deep sea is always poured from right above regardless of a solar position for dispersion and refraction. Moreover, there is also little change of light volume to sunset. Therefore, there is also much deep sea fish with the tubular eye which has turned to right above. In the sea deeper than the depth of water of 1000 m, light hardly arrives. Therefore, there are much deep sea  fish where eyes degenerate and which does not have eyes, and deep sea fish whose eyes are very small.
There are many kinds which emit light in deep sea fish. A bioluminescence is a luminous phenomenon which happens by a chemical reaction, and is one of the important features which many deep sea living things have.
It is supposed that a number of individuals is used and 90 percent or more emits light 70 percent of the deep sea fish which lives in the sea deeper than 500 m.
Deep sea fish captures food by emitting light, or takes deep sea fish communication.