ELY5: Fish have special lungs called gills, which are like a stack of delicate tissue paper, with many layers of thin tissue all sitting next to each other. The surface of each tissue paper needs to not touch its neighbours in order to absorb oxygen from the water. If you soak a stack of tissue paper in water, and then take it out; it will be impossible to peel the tissues apart. This is exactly what happens to fish gills once they leave their water home.
phrenos t1_iy4v7m7 wrote
Reply to ELI5: why fish can’t breathe in air despite air having plenty of oxygen by CR1MS4NE
ELY5: Fish have special lungs called gills, which are like a stack of delicate tissue paper, with many layers of thin tissue all sitting next to each other. The surface of each tissue paper needs to not touch its neighbours in order to absorb oxygen from the water. If you soak a stack of tissue paper in water, and then take it out; it will be impossible to peel the tissues apart. This is exactly what happens to fish gills once they leave their water home.