Parrotfish make themselves a kind of mucus 'sleeping bag' which masks their smell from predators and keeps parasites away.
4
Cymothoa exigua is a type of parasite that enters through fish's gills, eats their tongue, and then replaces it.
6
There is a disease called ichthyosis that turns the skin scaly like a fish.
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Before making Finding Nemo, the animation gurus at Pixar Studios had to take a graduate class in fish biology and oceanography.
13
Sharks, like other fish, have their reproductive organs in their chests.
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