I certainly hope so, I think I am personally keeping the mackerel population at manageable levels with the amount that we consume in our household! The book says that oily fish is allowed at all stages due to the good benefits outweighing the fact that they are high in fat
I confirm that smoked mackeral is absolutely fine... all oily fish is great for us just, if you're buying tinned versions ever, avoid those in oil / sauces etc. Find natural ones.
Sugar free jellies are fine. I read somewhere to make themselves up yourself rather than buying the ready made ones for fewer carbs. They're cheaper anyway and as people often complain at the cost of this diet, why not make them up. Three portions per day ok, and one sachet makes four, I believe.
I love mackerel, but I think without veg and potatoes it just doesn't agree with me, I had a terrible time eating it as it repeated on me all day and I felt awful, so I shall have to have something a bit lighter in taste.
In the book I'm sure you can't have oily fish when you reach stage 3.