Do any animals or fish have a "built-in" light source so they can see in the dark?
by 
headscratcher1
ANSWERS: 2
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Yes. It's called bioluminescence. Marine life in the deepest parts of the oceans often generate their own light. See: http://www.seasky.org/monsters/sea7a3.html http://www.mbayaq.org/efc/efc_mbh/dsc_about_survival.asp
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WHile it is true that a number of the creatures in the deep deep sea have built-in light sources (Hungry Guy's answer is correct), these light sources are typically not used for general vision purposes. Like a firefly, the lights are often used to find potential mates. Alternativey, the lights are often used for hunting. Many small creatures are attracted to lights as it is not uncommong that really small things in the ocean light up, too (plankton, for example). As such, a larger predator will have small lights that are used to lure in prey. At that depth, light simply does not travel far. Even at 100 feet, a typical diver's light that is blinding on the surface barely illuminates the reef a couple of yards in front of you.
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