salmon has a higher than 5% fat content so normally would be classified as an oily fish . The significance of this for freezing is that is has ta lower water content and is more susceptible to freezer burn. Once the salmon stays in the deep freeze and there are no temperature fluctuations it wont kill you to eat it after keeping it for longer than 3 months, the texture of the fish flesh may have changed and the taste may be a little blander.