Is it ok to reheat fish?

I never really like my fish reheated because I get paranoid but my mum reheated the food from the fish and chip shop before I even got a chance to ask whether it couldn't be reheated. It was from the fish and chip shop and had cooled down so she did it for about 30 seconds in the microwave, when I was eating it it may have not felt boiling but steam was coming out when I cut open the fish.