A barrel-eyed fish, it perceives the world through two eyeballs located deep in the transparent head.
The bodies of these fish do not have any special structure to resist the tremendous pressure of thousands of tons per square meter. Basically, they are not against pressure, they are simply “conforming to nature”.
It’s like the human body under atmospheric pressure, in fact, as you are reading this article, your body is under pressure somewhere around 10 tons per square meter. However, you cannot feel it because the pressure from the environment presses in and the pressure from your body to squeeze out is equal. Think of your body’s pressure as the equivalent of atmospheric pressure, equal to 1 atm.
When you dive into the water, in addition to atmospheric pressure, your body will suffer more water pressure. At this time, the ambient pressure will be greater than the body’s pressure, so it will press on your body. The deeper you dive, the larger the pressure difference will be, and the stronger the pressure on your body will be.