a lot of people likes 8" inches to keep. If we are catching a lot of perch we will sort 8" or bigger to keep and throw the smaller ones back. but if you are into some decent size perch some will keep only 9" or bigger depends on what you want to clean and how fast you want to get off the lake.
You'll get a lot of different answers on this one. It varies from west to east as well. Personally I don't like to keep anything under 9". However if the fish isn't going to make it then I'll keep it if smaller. Fishing from deeper water (60'+) produces a lot more mortality than shallow water fishing, so that is a factor too. I suppose if you are good at cleaning fish then the smaller ones are ok, but I'm not and it just seems like such a waste.
Nine inch minimum on my boat. I have some 9" measuring sticks for those yhat also look at a 26" walleye as being FO 10#'s. You want to keep under 9", keep them in a separate bucket/cooler and stop fishing when you catch you limit. Deep hooked,,,,,feed the gulls as they are hungry too.