What is deep sea fish

What is deep sea fish? I can't answer. I have interested in deep sea fish. But  I didn't know deep sea fish in detail. So, I will introduce deep sea fish today.
Deep sea fish are fish which live in deep sea. Generally we call fish which live in water deeper than 200m deep sea fish. But there are many species ,for example one of the species change habitat depth in the process of glowing or one of the species swim vertical to chase food, so the word of deep sea fish didn't have clear define.It has estimated, if at least 2,000 or more sorts in the saltwater fish by which about 15,800 sorts  are known correspond to deep sea fish. These are roughly divided into two types of the deep sea fish, one of the it lives near the seabed, and the other of it separates from the seabed, and drifts and lives the middle layer, and the number of seeds contained in each is considered to be the same number. Since the lifestyles of  these two type of deep sea fish completely differ, respectively and the phylogenetic system on evolution is often reflected, in order to understand  and evolution and ecology of deep sea  fish, classifying and thinking of both is important . Since the plant which photosynthesizes does not exist in the deep sea which sunlight does not reach, it is animals and plants of a shallow sea that support the foundation of the food chain of deep sea. Finally remains and excrement of a living thing of a shallow sea lie on deep sea.It is consumed by floating deep sea living things, such as a krill and jellyfish, and also these organic matters that sink and go are used as an energy source of deep sea organisms, such as shellfish, a sea cucumber, a brittle star, after depositing on the deep ocean floor. It is preyed by the still  more large deep sea living thing on them, and they form the food chain in deep sea. The food chain in deep sea is formed with these organic matters that sink and die. Deep sea is the dark ocean space obstructed by a hydraulic pressure and low temperature very high to a degree. Moreover, the inside where the total calories which can be exploited are part of the calories which produced in a shallow sea. Since deep sea fish is adapted for the environment which can also be said to be this limit, to the fishes of a shallow sea, the special bodily structure and lifestyle which are not seen have been acquired  The average depth of water of the sea which covers 70 percent of earth surface amounts to about 3,800 m, and the sea deeper than  200m  occupies 93% by a volume ratio. When understanding the biodiversity which spreads there to be the environment of the deep sea which constitutes the greatest biosphere in the earth, the role which deep sea fish study plays is large.
There are introduction of deep sea fish. I study deep sea fish has many mystery and be a important existence to research sea. So,I have more interested in deep sea fish today.