This also works if the frozen pieces are whole fillets or smaller fish. I had 9 Bamfield springs to deal with and not much time so I filetted the fish and vacuum sealed the halves. Then when I had more time I cut the bags open, put the sides in a cooler for 4 hours, and wiped the bags out. At this state you can handle the fish as a still frozen slab,(no moisture) but it will CLEAN cut with a sharp knife.
Then reseal the smaller pieces and they look better than when they were freshly vacuum sealed. If your fish is whole go to a butcher and get him to cut steaks.