If your tuna has a very noticeable fishy smell to it there is most likely something wrong with it such as bacteria that can be dangerous to consume. It will be important to avoid eating any tuna that smells fishy because it has most likely gone bad. Instead you will want to throw it out and buy new tuna, perhaps from a different supplier.
You should pay attention to any expiration or ‘best buy’ dates that are on your tuna cans or containers, just so you will be able to know when to eat it by. Eating tuna that has bacteria in it could lead to food poisoning which can cause a whole variety of very unpleasant symptoms which you will want to avoid at all costs.