Apparently swim-bladders and lungs evolved from the same organ that kind of did both jobs.

Lungs are useful for a fish cus theres waaaaaaay higher concentration of oxygen in the air than in the sea and its easier to get.

Thats why aquatic mammals like whales and dolphins can *dominate* fish so badly. They can get way more oxygen and run a faster metabolism, the classic mammalian strategy of just being a super charged turbo killin' machine!


https://youtu.be/J7rN3_tSb7g