When you and I take a deep breath, we pull air into our lungs. That’s because humans are mammals. But fish aren’t mammals. They usually don’t breathe air. They usually don’t have lungs. That’s what I ...

Fish live surrounded by water, so the idea that they might struggle to breathe sounds wrong at first. It feels like asking whether birds can fall out .

We can be guilty of thinking that oxygen is a uniquely human need. While all land-dwelling animals breathe oxygen from the air, fish need oxygen too. Not only this, but fish can run out of oxygen, ...