this post was submitted on 22 Oct 2024
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There's not enough oxygen in water to support our metabolisms, even if we had gills.
Fish are adapted to conserve and use less oxygen, from slower metabolic rates to more options for anaerobic respiration that doesn't poison oneself from within.
I don't believe this. Sailfish, barracuda, tuna, huge mass, highly active... I'm sure they use a HELL of a lot more oxygen than I do on a good day. Gills extract MORE oxygen than lungs do, they're more efficient.
My unscientific opinion tho.
This article estimates at a 40kg sailfish uses about 2.7 megajoules per day of energy when hunting. That's about 650 kcal.
An 80kg human weighs about twice as much and needs about 3 times the energy, without even exertion.
Warm blooded animals spend a lot of energy just maintaining body temperature. Plus water doesn't have very much oxygen in it, compared to the atmosphere.
That last line is one reason we're able to fish successfully. Even large fish tire out because they can't pull enough oxygen from the water to struggle forever.