The deep ocean comes under aphotic zone. This means that it does not receive any amount of sunlight. Such oceans are often very cold, but life does exist at such hostile places.
Animals that live at deep oceans have some special characteristics that are helpful to survive at great depths and in freezing conditions. Organisms at such deep oceans are able to withstand the high water pressure. They are also able to hold their breath, for very long time. Such organisms may either obtain their food from the photic zones or from the sinking remains of the other dead animals, of the photic zones.
Moreover, some of these animals are chemosynthetic. This means that they are able to produce their own food without light or photosynthesis. Some are able to produce their own light in these completely dark places.