Bioluminescence — an Incredible Game of Evolutionary Cat and Mouse
Yes, you are looking at a fish that appears to be spitting light and yes, it is completely amazing, like underwater fireworks, or fish lasers:
…However! The truth is far more fascinating…
What you’re seeing is the defense mechanism of a tiny crustacean called an ostracod, a shrimp-like organism about 1mm in size that some fish accidentally eat while hunting for plankton. When eaten by a 
translucent cardinalfish, the ostracod immediately releases a bioluminescent chemical in an attempt to illuminate the fish from the inside, making it immediately identifiable to predators. Not wanting to be eaten, the cardinalfish immediately spits out the ostracod, resulting in little underwater fish fireworks. THAT’S CRAZY!
[First 3 images from the BBC 2 show; Super Senses: The Secret Power of Animals]
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