My fish stop all the time, but I don't know what will happen if they stop for half an hour.
If the fish are fresh water fish the kidneys would not work. The fish would die.
They die
they will die
If chinstrap is a fish, then no. Fish actually don't sleep!
they drown
Fresh water fish survive just as well as fresh water fish. Maybe this question isn't the one that you actually meant to ask?
it would eventually shock the fish and kill them
the fish needs to be in warm water that is just right. then leave the fish alone in peace and it will be fine.(:
it dies
They die.
If by clear water you mean freshwater than the fish will have all sorts of problems. It will be more likely to get a disease, stress the fish out, weaken its immune system, and will kill the fish.