Marine Science Chapters


Deep-sea Water Column

Hatchet Fish
Deep-sea hatchet fish have light organs on their underside to disrupt their outline from predators viewing them from below. They hide in the twilight waters, with eyes looking up and a mouth set so that they can strike from below in the water column, then sink back to the area of twilight. They are not able to see below them but rely on their soft glow to match their color to their surroundings and camouflage what would be seen from below.

Fish are the main inhabitant of the deep-sea water column. These fish may have weak bones, soft flabby flesh, and bioluminescent organs. The bioluminescent organs may be used by fish living in the twilight areas to light up just enough so that they are not easily seen from below.

Angler Fish Two Angler Fish, one with distended stomach
Deep-sea angler fish show the large mouth, distensible stomach, luminescent lure and black-lined stomach adaptations of deep-sea fish. The angler fish on the left shows the lure (red tip). The two angler fish on the right show how it looks when the stomach is distended.

Some fish have a large mouth, distensible stomach, luminescent lure, and a black-lined stomach as adaptations to a habitat with a reduced food supply. The large mouth is so that they can take in large prey if it is encountered. The distensible stomach is so the large prey can be completely consumed. The luminescent lure is to attract prey. The black-lined stomach is so that once a bioluminescent prey is consumed it will not 'light up' the predator's distended stomach and make the predator easy to see by other predators.

Viper Fish

Viper Fish Mouth
Deep-sea viper fish (top) and close up of fearsome teeth (bottom).

Most deep-sea fish are small but with fearsome teeth. The majority of the deep-sea fish are less than six inches. This small size reduces their need for a lot of food. Their teeth don't give their prey much of a chance for escape and may even make it hard for the fish itself to close its own mouth.

Myctophid Fish and other DSL species
Myctophid fish and other DSL species. The red ones are crustaceans.

The DSL (Deep Scattering Layer) appears as a false bottom that moves to the surface every night and drops to the depths in the morning. This layer used to show up on fathometer readings, making captains fearful about what the real depth of the water was ... but it was found to be a reflection from the gas bladders of some of the fish in this layer. The fish and crustaceans that make up this unique layer of deep-sea critters hide all day in the dark depths, expending energy every night to come to the surface to feed in the productive waters, then to return to the safety of the depths in the morning. By living in the cold deep-sea these species may not need as much food as their surface counterparts because they may drop their metabolism to low levels in the cold depths of about 800 meters or so.

 Copyright and Credits
(Revised 11 October 2004)
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