Watch as you are reeling in a fish. If it does not take long to reel it in, and it comes in very easy without any line tension, it will be a small one. If the tension bar remains at yellow for a long period of time it will be an average size fish. For a huge fish, if the tension bar goes red do not reel it in immediately. Make circular motions with the Analog-stick and the fish will tire as you reel it in.