You can also "pre-coat" them with whatever you normally use, then freeze them ... and they don't "burn" then, either.

Frost on them just means the moisture is leaching out of the fillets ... they aren't "freezer burned", yet. Freezer burned fish will turn a dirty white, and the freezer burned meat will be tough.

If you're using a vacuum sealer ... what you may want to do, in the future, is not seal the bag so close to the fillets -- leaving a couple two or three inches of bag past the edge of the meat. Then, if/when you see that the seal is compromised and the bag has taken on some air .... open the sealed end and then re-seal the frozen fillets, in the same bag. The thicker the plastic, that your sealer uses, the more likely it is to stay sealed. The thinner, cheaper plastics, of the cheaper model vacuum sealers, don't hold a seal quite as long .... so leaving a "tag end" section of extra bag will allow you to re-seal, if necessary.

........ cp