Fresh fish should be frozen as soon as possible after being caught. Before freezing, prepare the fish by cleaning them and cutting them into fillets or steaks. The National Center for Home Food Preservation recommends pretreating the fish by dipping in an ascorbic acid solution or brine solution before freezing to improve the quality of the thawed fish.
Place fish fillets in freezer bags in a single layer. Remove as much air as possible from the bag and seal it tightly.
Place bags flat in the freezer for about six hours or until they're frozen solid.
Fill another freezer bag about one-third full of cold water. Add frozen fish fillets until water barely covers the fillets on top.
Place the bags immediately back into the freezer, arranging them so that all fillets are completely covered. Freeze until ready to use.