answer is get it to your taxidermist immediately. While that is not always an option, the fish can be kept on ice until it's brought in if it will be for a short time. (Less than 12 hours, depending on temp.) If you are going to freeze it for any amount of time, I prefer this way. Soak a towel with water and wrap around your fish. Protect the tail from being bent if possible. Place that soaked towel with your fish in a plastic bag. Wrap the bag tight and seal with tape. Place fish in the freezer until you can get it to your taxidermist.