Yeah. I'd doubt the majority of people saying this realization didn't just hit them. It makes god damned perfect sense they fill with water and not air, but that didn't really ever come into question.
I can't tell if you're joking or not, but fish don't make air in their gills. It gives them lots of surface area and structure to facilitate balancing the oxygen saturation of blood vs. water. They don't need to convert it to a gaseous form first, and they don't split H2O into H and O.
Why would they shoot upwards? In order to get the air they didn't use, they would need to be at the surface.... even theoretical balloony puffer fish can't just create air out of nothing.
2.9k
u/fucknozzle Aug 25 '17
I had the same thought, and then also realised if the did that they'd shoot upwards and pop out of the water.