Well, a fish that hangs from a Sim's shoulder down to his knees when caught, magically becomes just large enough to fit on a small tophy mounting. If cooked, it also magically makes exactly one portion on a plate (when cooked for one) -- or magically expands to make six of the same sized portions (when cooked for a family).
For the jumbo fish, I recommend the "make many / group meal" option - you'll get two platters out of them.