The mesopelagic zone is from 200 m to 1000 m in depth, and fish in this area have adapted by being small, but with large mouths, and highly varied diets (Ocean, 2004). They have developed adaptions to reduce their metabolic rate; have lost their swim bladder; developed soft, weak bones; have lost scales and spines; and have developed flabby, watery flesh. Many have developed photophores (light organs) that produce bioluminescence. Examples of mesopelagic organisms includes ostracods, copepods, krill, shrimp, jellyfish, squid, siphonophor4es, and some fish. Fish include the headlight fish, Diaphus theta, the pearleye, Bentalbella dentata, and the barreleye, Macropinna microstoma (Yancey, 2004).
The bathypelagic zone goes from 1000 m to 4000 m where the sea is completely dark, so many organisms have developed bioluminescence (Ocean, 2004). Many organisms have reduced eyes or are completely blind. Because of the scarcity of food at these depths, fish are extremely small, have flabby, watery muscles and weak skeletons. They have no scales, and poorly developed respiratory, circulatory, and nervous systems. They have large mouths. Bottom dwellers include polychaetes, bivalves, crustaceans, sea cucumbers, and brittlestars. Fish found here include the eelpout, Pachycara bulbiceps, the Cuskeel or Brotulid, Sciadomus pedicellarus, and the viperfish, Chauliodus macouni (Yancey, 2004).
The abyssopelagic zone runs from 4000 m and 6000 m, and the fish in this zone have large heads and tapered tails (Yancey, 2004). They usually have degenerate eyes. Some develop bioluminescence to attract prey and for communication and courtship. Rattails have swim bladders to allow them to float above the sea bed. The deepest known fish are the brotulids, Abyssobrotula, found in trenches at over 8000 m. Rattail or Grenadier fish are the most common fish found in the abyssopelagic zone. The deepest dwelling skate, Rajella bigelowi, is found...