<P> These animals have evolved to survive the extreme pressure of the sub-photic zones . The pressure increases by about one bar every ten meters . To cope with the pressure, many fish are rather small, usually not exceeding 25 cm in length . Also, scientists have discovered that the deeper these creatures live, the more gelatinous their flesh and more minimal their skeletal structure . These creatures have also eliminated all excess cavities that would collapse under the pressure, such as swim bladders . </P> <P> The lack of light requires creatures to have special adaptations to find food, avoid predators, and find mates . Most animals have very large eyes with retinas constructed mainly of rods, which increases sensitivity . Many animals have also developed large feelers to replace peripheral vision . To be able to reproduce, many of these fish have evolved to be hermaphroditic, eliminating the need to find a mate . Many creatures have also developed a very strong sense of smell to detect the chemicals released by mates . </P> <P> At this depth, there is not enough light for photosynthesis to occur and not enough oxygen to support animals with a high metabolism . To survive, creatures have slower metabolisms which require less oxygen; they can live for long periods without food . Most food either comes from organic material that falls from above or from eating other creatures that have derived their food through the process of chemosynthesis (the process of changing chemical energy into food energy). Because of the sparse distributions of creatures, there is always at least some oxygen and food . Also, instead of using energy to search for food, these creatures use particular adaptations to ambush prey . </P> <P> Creatures that live in the sub-abyss require adaptations to cope with the naturally low oxygen levels . </P>

Where does the food for most deep sea animals come from