I fish to eat. It is not a sport to me. So I eat 100% of what I catch - or in other words, I only catch what I want to eat! I am always in "trout country". I personally would not even eat meat if I felt moral qualms about catching and killing it. Everyone who eats meat should come to grips with this fact of life. I am not advocating one or the other - just it is hypocritic to eat meat and not want to do the "dirty work" yourself.
Little fish less than 4-5 inches - fry them up crispy and eat the whole thing.
Medium fish (ones that fit in my small frying pan) - prefer to cook on coals but if fires are not allowed II turn down the heat on my stove as much as I can, put a lid on the fry pan, and move the frying pan by hand to even out the heat. I cook in olive oil. I find that a frying pan with teflon is much better than little backpack frying pans. I buy a cheap light teflon coated fry pan and take the handle off. The hard thing is to find a light lid that fits the pan.
Ok, this may offend some -- but when you fry a very fresh fish, they will curl up in the fry pan (residual muscle response) - if you make slices along the backbone, they will stay flat.
Big fish (too big to fit in my frying pan) -- filet and fry. I have also experimented with boiling the fish, de-boning and then frying the meat. It is OK but not great. If you are going to boil fish, you should just make fish chowder. (add a pack of corn chowder soup). Also, on a big fish, there is a small round pod of meat in the cheek by the gills - it is really tasty.
In the past, when fires were more prevelant, we would smoke fish and then use it for trail food. It is a lot of work and not something you would do if you are trying to "make miles" on the trail.
I almost was able to cook biscuits in my bear cannister - not quite hot enough. I should try to cook fish in my bear cannister! Bear cannister fish jerkey?