WHAT KIND OF WIZARD FISH IS THIS
DUDE THATS A BABY KAIJU
SCIENCE SIDE OF TUMBLR URGENT
What you are seeing here is not just one fish, but two different organisms! The fish (a cardinal fish, I believe) has just attempted to eat an ostracod (a small crustacean). When threatened, the ostracod produces the chemicals luciferin and luciferase, which emit a light when they’re mixed. This process is called bioluminescence.
So, why does this make the cardinal fish spit out the ostracod? Well, both the cardinal fish and the ostracod dwell deep in the ocean, where very little light from the sun reaches. Through bioluminescence, the ostracod is essentially producing a bright “warning light” to BIGGER predators that the cardinal fish is nearby. So now, the predator cardinal fish could become easy prey for something else! To save its scales, the cardinal fish spits out the bright ostracod and swims away, back into safe, inky blackness.
You can kind of see the tiny ostracod fall down the side of the aquarium wall in the gif above, while the bioluminescence chemicals disperse in the water.