How should I wrap raw fish for freezing?

It should be tightly wrapped, ideally with oxygen-proof, vapor-proof cling film. Prepackaged, raw, unfrozen fish sold in stores is generally wrapped using a process called modified atmosphere packaging (MAP). The air in the package is replaced with gases such as nitrogen that don’t interact, like oxygen does, with food components. Products wrapped this way may be puffed up on top by this gas. Fish should not be frozen in this type of packaging because water can migrate from the food to  the head space (the bubble)  created by the gas; the result will be dehydration and freezer burn. Also,  the plastic wrap over the head space can tear if something heavy is placed on it. Then product will dry out and develop freezer burn. 
 
Source(s):
Susan Brewer, Ph.D. University of Illinois, Department of Food Science and Human Nutrition