How is fishing and boxing considered exercises?
Apparently you have never boxed, because if you did you would know that it is a supremely demanding sport that requires an extremely high level of fitness. In my 20's I was in pretty good shape and got in the ring for fun. I couldn't last two minutes before I was gasping for air.
Fishing as exercise, is not not very demanding however you are constantly casting and retrieving which probably burns a few calories. If you use a kayak, canoe or rowboat you will get exercise piloting the boat. If you are fishing from shore the hike to your fishing location and walking between various locations will provide some exercise. At least it's better exercise than sitting on the couch.