Looks like Henneguya salmincola (a myxozoan parasite). My literature says it doesn't affect the flavor, texture, or safety of the meat, but it sure doesn't look very appetizing. The parasite is also found in rockfish and flatfish.

The other possibility is Kudoa spp. which is also a myxozoan parasite. It forms large white patches or streaks in the flesh and will cause the meat to breakdown if even it meat is smoked.