Some deep-sea fish have been known to explode as they are brought to the ocean's...

[Ryoma Echizen]

...surface. How do pressure chan Some deep-sea fish have been known to explode as they are brought to the ocean's surface. How do pressure changes cause this to happen?

[J D]

Fish have a swim bladder filled with air (evolved into our lungs) they use to maintain neutral boyancy. It you reduce the pressure by half, the volume of the bladder doubles, and kaboom.

[astatine]

when you go scuba diving, one of the first things you learn is that when you ascend, you keep breathing. you never hold your breath while you surface. Otherwise you may experience embolism where your lungs can explode.

If you're 100' below water, the pressure is 4 times what it is at the surface. If you ascend without air leaving the lungs, the volume of the air expands to 4 times what it was at a 100' and, guess what, bad things happen to you. P1V1/T1 = P2V2/T2, with temperature probably not changing much if it's a quick ascent.

Note - this is not the "bends" that you hear about that divers can suffer - that's a different beast.
To answer your question, if the fish had a cavity with a gas, the same phenomenon will be magnified even more because of the depth of the fish.

[(Ohm)Mistress Bekki]

PV = nRT

So all other things being equal, volume goes like 1/P

So when pressure goes way down, volume goes way up. Boom.

Also, dissolved blood gasses can come out of solution if the pressure decreases rapidly, resulting in a very unpleasant death for fish or divers. There's a good James Bond scene where the villain puts a victim in a pressure chamber, cranks it up for a while, and then evacuates it. The guy pops.