Deep-sea fish is a pond term for fish that live in the shadows below the surface of the sunlit waters, that is, below the epipelagic or photic zone in the ocean. By far the lantern fish are the most abundant deep-sea fish. Other marine fish include the flashlight fish, cutting sharks, bristlemouth, anglerfish, viperfish, and several species of eelpout.
Only about 2% of marine species are known to inhabit pelagic environments, compared to benthic organisms that live in or on the seabed. Deep-sea organisms generally inhabit the bathyal zone (1000–4000m depth) and the abyssal zone (4000-6000m depth). However, characteristics of deep sea organisms, such as bioluminescence can also be found in the mesopelagic zone (100-2000m depth). The mesopelagic zone is a dysphotic zone, which means that light there is minimal but still measurable. The oxygen-poor layer is between 700m and 1000m deep depending on its location in the ocean. This area is also the place where food is most abundant. The bathyal and abyssal zones are aphotic zones, meaning no light penetrates this area of the ocean. These zones make up about 75% of the habitable ocean space.
The epipelagic zone (0-200m) is an area where light penetrates the waters and photosynthesis occurs. This zone is also known as the photic zone. Because this zone is usually only a few hundred meters deep underwater, the deep sea, about 90% of the ocean’s volume, is in the shadow. The deep sea is also an extremely hostile environment, with temperatures rarely exceeding 3 °C (37.4 °F) and as low as −1.8 °C (28.76 °F) (the exception being hydrothermal vent ecosystems which can exceed 350 °C, or 662 °F). ), low oxygen levels and pressures between 20 and 1,000 atmospheres (between 2 and 100 megapascals)