I know it can be confusing at first, there are a lot of things to learn and this is made worse by the fact that there is a lot of outdated and just downright wrong information out there. Many GPs (and so-called "diabetes nurses") have a limited and somewhat out of date knowledge of diabetes - so your doctor won't necessarily give you the best advice. Also Diabetes UK publishes some pretty dubious information. So... how do you know who to believe? I suggest that you start off by talking to knowledgeable patients. They have been through it all, and are very highly motivated to find out the best possible healthcare strategy. Fortunately, you have come to the right place - this forum has lots of such people on it (as well as a sprinkling of professionals).
So, if you look around these forums you will find lots of good advice on diet - for example you might like start out by reading the "
Newly diagnosed and so confused" thread. If you have a lot of time, then another thread that is worth reading is the
NEW COMPLICATION !!! thread. This is bit long, and you have to ignore the odd outbreak of a minor flame war, but if you persevere there is a lot of really useful information in there.
Once you start to get to terms with this, I suggest that you get some books. There are some great books out there (as well as some dodgy ones) - you will see references to several in various postings, or you can always post yourself to ask for recommendations.
Lastly, about the smoked fish. I have never heard of this causing any problems specifically to diabetes management. There have been minor health scares suggesting that since there are carcinogens in smoke, smoking food isn't necessarily a very good idea. However, I have never seen any real evidence that smoked fish causes any health problems. So, since smoked fish is seriously low carb (which is what you should be aiming for) - I suggest that you eat as much of it as you like!