First, it is important to know that frozen fish doesn't "go bad"—that is, it won't make you sick if it's been in the freezer too long. Then what, you might ask, is too long? Fish will not keep its same flavor and texture indefinitely, so when we talk about lengths of times for freezing, it is about keeping the fish at good eating quality.
Just be sure to wrap it well. Its best to wrap individual portions in several layers of plastic, and press the plastic close to the flesh to remove as much air as possible. Put the individually wrapped portions in a freezer-weight plastic storage bag and label the bag with the name, size and date of contents.