DEEP-SEA PAGES:
MESOPELAGIC (MIDWATER) and BATHYPELAGIC ANIMALS

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Most of these photos are mine, others are ones I took from the ROV Oceanic Explorer's or Alvin's cameras.

• Pelagic animals are those that live in the open water, not closely associated with the seafloor. [Benthic and benthopelagic (bottom-associated) animals are found on most of my other animal webpages (use the menu, upper right)]. Animals in the deep pelagic--fishes, jellies, shrimp, etc.--must adapt to low food supplies. They eat each other, and/or the detritus falling down from above. Some species are vertical migrators--they migrate to the upper waters at night to eat where there is more food. Animals often have gelatinous tissues and overall very low protein contents, with relatively weak muscles*.
  
• Many camouflage their bodies by being transparent, black or red. Red light from the sun does not exist in the midwater twilight as red wavelengths are absorbed (removed) strongly by water (and blue the least, hence the ocean's color). Consequently, most deep-sea animals have lost the ability to see red.
  
• Many have have special adaptations to cope with low light levels, such as large eyes and photophores (light-producing organs) to produce bioluminescence for headlights, lures, mating signals, camouflage (counterillumination; see below), confusing prey, confusing predators, and/or "burglar alarm" (light up your predator to attract a higher-level predator to the one after you). About 75% of mesopelagic organisms are bioluminescent. Most bioluminescence is blue, or less commonly green, since blue wavelengths of light, followed by green, travel farthest in water (red light, in contrast, travels the least, its energy being absorbed by water most easily).

Many deep-sea fish have elaborate mechanisms for catching food presumably because it is so infrequent: devices such as those noted above--light lures, large eyes (some focused forward or upward for silhouette detection)--but also huge teeth, and expandable jaws and stomachs that allow them to swallow prey larger than themselves (see examples above and below). The telescopefish is a prime example (see above right and far right-->). To see how it uses its forward-facing tubular eyes, see the MBARI video here.

*Our Fish Research: In the 1980s we found that some midwater fish have buoyant gelatinous layers (see below: gel layer just under skin in the blacksmelt cross-section). They also have very low protein content in muscles. These are probably adaptations to an energy-poor environment, and/or the lack of light, which may make it a waste of energy to have robust muscles for long pursuits or escapes. It also means these are not very good for human consumption.

Our publications on midwater fish anatomy and biochemistry:
--Siebenaller, J.F., P.H. Yancey (1984). The protein composition of white skeletal muscle from mesopelagic fishes having different water and protein contents. Mar. Biol. 78: 129-137
--Yancey, P.H., R. Lawrence-Berrey, M. D. Douglas (1989). Adaptations in mesopelagic fishes. I. Buoyant glycosaminoglycan layers in species without diel vertical migrations. Mar. Biol. 103: 453-459
--Yancey, P.H., T. Kulongoski, M.D. Usibelli, R. Lawrence-Berrey, A. Pedersen (1992). Adaptations in mesopelagic fishes. II. Protein contents of various muscles and actomyosin contents and structure of swimming muscle. Comp. Biochem. Physiol. 103B: 691-697

TO FIND almost any FISH SPECIES in the world, go to FISHBASE.
MORE DETAILS on DEEP SEA FISH can be found at Jeff Drazen's U. Hawai'i site

Thanks to Ruben Pohl for the FISH depth ranges listed first as peak abundance, followed by record depths. Other fish depths from FISHBASE (above).

Viperfish often have teeth so big, they need a slot in their jaw/skull (see Chauliodis photo) so they don't cause self-injury! From submersibles they have been seen hanging motionless with their lure over their mouths, waiting for prey (see Randall and Farrell book below ).