i practice mostly catch and release fishing. I don't know until I catch the fish if it's worth keeping..
I fish in an area with very protected populations of fish, in an area that is managed cooperatively for protection of trout. The water is released at a controlled rate from the bottom of a dam to provide year round cold clean water to maintain trout populations, brook, brown and rainbow. There are 100 million people within a 2 hour drive of this river. It still contains wild brook and brown trout and is stocked with rainbow trout. It has strict catch and release rules for a stretch below the dam, and beyond a point you have a creel limit. I fish because, as others mentioned, you are honing a skill that is related to survival. That feels good. It feels good to be in nature.. it is also a good way to get away from people. Tons of people walk trails but far fewer walk in the river. I get to see beavers, heron, deer, eagles and hawks, mink, otter etc. And moving slowly in the water keeps them from recognizing you as a threat..
Most importantly.. I don't know what I'm going to catch until i go out and catch it.. If i catch a native brook trout, any size at all, i'm not going to keep it. They are fucking sacred and beautiful and the fact they are still here is a testament to the quality of the habitat and our preservation of it. If i catch a big brown trout, I let it go, because it could breed and produce a lot more fish. If i catch little brown trout, too small to eat, I let it go, because it plays an important role as a food source for the heron, mink, otter, large fish, etc. I will, one to two times a year, keep a brown trout that is mid-sized. I don't want more than I can eat in a meal. I eat the whole thing, no waste. I know its full of agrichemicals, but it feels good. If i catch a rainbow, I will always consider eating it, because they don't overwinter or breed as successfully as the native brook and wild/naturalized brown trout.