It sounds like its called clamped fins, they are probably stressed. Did you just buy them?
Can u give us the specs of your tank (size, fish residents, water parameters, and how long it been running)
When I first got my angel fish they spent time hiding and my white one had clamped fins for while. I didn't use light for 2 day and gradually they came around and now they are all brave and would eat bloodworms out of my fingers.