One point worth considering about tinned tuna is that when it's canned, the fatty acids are reduced to levels similar to white fish. This is because tuna is cooked before it’s canned and most of the oil is lost during this process. So, although canned tuna is a healthy choice for most people, it doesn't count as oily fish
(other canned fish such as salmon, sardines, mackerel, trout and pilchards all count as oily fish when they're canned because the canning process doesn't significantly reduce the fat content of the fish, some of them also have a lot of calcium from small bones) http://www.eatwell.gov.uk/asksam/healthydiet/fiasandshellfishq/#A221141
I prefer oil as the whole purpose of eating it is for the oily fish qualities, surely?
Another tip, I usually squeeze lemon juice over all my fish now; good for keeping your BG down apparently. Makes the tinned stuff a bit more palatable too.