My husband recently caught lake trout from Priest Lake and we they cleaned the fish there were what looked like blisters on the flesh. Do you know what the blisters are and are the fish safe to eat?

Our guess would be a small parasite - possibly a copepod.  They cause ulcerations on fish that lead to what appear to be pustules and open sores.  There is no risk to human heath if the fish is cooked properly.  Many times, as the sores heal, there will be scar which look like grains of sand.