You’ve all seen the images of the weird looking fish with a light bulb hanging over their head. This fish lives in a deep part of the ocean, where it is too dark for humans to see. And this is not the only fish there. A lot of fish that live down there use a natural light from their body to attract prey, mates or scare of an attacker. It’s a fascinating process, but how does it work exactly?
The process fish or other creatures use to light up parts, or their whole body, is called bioluminescence. It is essentially a chemical reaction that is happening inside of the body. For this to happen, the creatures have to posses a certain molecule that is called luciferin. This molecule reacts to oxygen, and when this happens, it produces a bright light. A lot of animals can also control this by regulating their chemistry and brain processes. They do this depending on their needs. If they have to scare off an attacker of some sorts, they can produce it faster. This is because their life is on the line and they need to react fast. When attracting mates or prey, they can take their time with it because they are not in immediate danger.
But this phenomenon isn’t only apparent in fish. There are a lot of sea creatures who have the ability to be bioluminescent. These creatures range from bacteria and algae, crustaceans (like crabs and shrimps), fish and even some sharks. It also differs where the creatures light up. Some have cells that produce light on their sides, underbelly, the tip of their tentacles, surrounding their mouth or some can even produce a fluid they shoot out of their body like some sort of bomb.
The same goes for the fact that this is a deep sea thing. It is true that this is most common in the deep sea. It is also where you can see it best, because it is dark there all the time. But this is actually not the only place where creatures can do this. There are also some small plankton who can produce bioluminescence. These creatures though, are most often found on surface level places. For example, there is a beach in the Maldives (on Vadhoo Island), where the bacteria makes the waves light up when they break. You can only see this when it is also dark outside though.
There is also a reason why we see this process, and the colour of the light, in a blue/greenish colour. This has to do with different wavelengths of colours. How shorter the wave-length is, how farther you can see it. This is because the electromagnetic waves of shorter wavelengths don’t change much from the barrier of the earth’s atmosphere, so the distances short wavelengths can travel is way farther than long wavelengths. The distance to the deep sea from the surface is obviously very long, so the long wavelengths cannot travel this far.
An example colour for long wavelengths is red, while on the other end of the spectrum, blue has the shortest wave-length. So this is the reason why the light we see from the deep sea fish is in our eyes always a blueish/greenish colour.
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