Adaptations to Life in Perpetual Darkness & Anglerfish Tidbits.


      In the vast depths of the ocean lies an unseen unsullied world; filled with utter darkness, little food, and distinct creatures that call this wintry place home.  The organisms that inhibit the ocean below the Mesopelagic zone have to adapt and develop certain characteristics to insure survival.

                                     Deep sea Includes: Bathyal, Abyssal & Hadal Zones


        Many deep sea organisms are black in color since the lack of light would negate the use of *countershading. Some fish are also red which is also unseen in this environment. Due to *bioluminescence the deep sea is not completely dark, thus deep sea fish still have functional eyes, however, they are much smaller and some creatures from the darkest depths are completely blind.  

       Food is also in short supply, thus deep sea fish often live sedentary lives; they lack swim bladders and have weak muscles; thus conserving as much energy as possible, until a meal comes along.  Then, they use their large mouths and expandable stomachs to accommodate larger, yet infrequent meals.

       Anglerfish are an example of a deep sea organism that has evolved to live in the shadowy depths.  They often have massive jaws and wait patiently for unsuspecting strangers to explore their world.

Although Anglerfish look unsightly and daunting most are relatively small, the smallest being ¼ of an inch.

      Anglerfish have developed an interesting use of bioluminescence to lure and capture prey.  The spine on their dorsal fin has been adapted into a motile fishing pole of sorts that they dangle in front of their mouths. At the end is a piece of exposed tissue that acts as bait. There are bacteria that live inside the fleshy tissue giving the bait its glow which attracts the anglerfishe’s prey.

        Finding a mate in the deep sea can prove even more difficult than finding food. Many species have either become hermaphrodites, employ the use of bioluminescence, or use chemical attractions to find mates. The female anglerfish release pheromones into the water that get the attention of the male anglerfish. In some species, including Cryptopsaras Ceratias, the anglerfish have developed a surefire way to ensure finding a mate.  The male anglerfish, which is dwarfed in size, has one sole purpose in life, to find a female anglerfish. Once he encounters her, he will bite into her where he will remain attached for the rest of his life. This ensures that they will be able to reproduce when necessary. In some anglerfish species the male will actual fuse to the female and connect their circulatory systems; having the female feed him. This is often called male parasitism.

 *Countershading is the coloration of fish with a dark back & a light colored belly; this works efficiently to allow fish to blend in while in open water. Thus when you see the fish from above you see a dark color that blends in with the dark ocean below and when you look at the fish from below you would see a light color that blends with the coloration of surface water.


*Bioluminescent is the production of light by a living organism. Fish in the deep sea use this for communication, to lure prey, for mating rituals, and so forth.


Feedback: what interesting tidbits do you know about marine life?  Have you had any personal experiences?

Author:  Ashley Tyer

“Although I’ve had many… Gods knows I’ll have more…”

Reference: Castro, Peter; Huber, Michael.  Marine Biology Eighth Edition. The McGraw-Hill companies. New York, NY. 2010


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