When freezing fish, Freeze in Water with a tablespoon of salt. You can take them out of the freezer up to a year later and they still taste like they were swimming yesterday, They will NEVER freezer burn.
Second tip.
Shark can tend to have a very strong "ammonia" smell and taste. I am told that this is because when they become excited or agitated they will actually urinate thru their skin. To prevent this you should always gut a shark immediately after catching (and deciding if he is a keeper),, then, once cleaned..soak the meat in either milk, as suggested by another user or in icy salted water for up to 24 hours. I also suggest a marinade containing, lemon juice, tequila and lime while cooking.
