I like to keep 7.5 inch for gills and I don't eat crappie. The reservoir I fish is awful for nice size gills...way too many. I would think that killin' everyone I catch wouldn't even put a dent into the population...so I let them all go. The ODNR just electro-shocked it and they said there are way too many small gills and way to many shad....but the bass and pike are really big...In one pass they shocked up 180 bass over 12inch. Tried for find the sturgeon they put in and found none...but was no surprise. Only have 5 seconds from timed shock... and sturgeon are too deep for that and they shocked the edges.
i just kind of give the fish a visual look over and if it looks worth keeping i put it on my stringer...my stringer only holds 8 fish so if i fill it im done keeping fish for the day...but yeh i jsut kind of visually estimate if i think the fish is worth keeping for fillets cuz i only fillet my fish...i never really measure the panfish i keep...just if they look big enough to get a decent size fillet....so in the end i rarely keep bluegills b/c i never get good fillets from them...most panfish i keep are white bass and crappies.
I have 2 small pieces of Electirical tape at the bottom of my pole. One is 10" from the base and the other is a little over 15". 1st is for crappie and second is for Walleye. Comes in handy when I'm wearing waders.
i keep 6+ bluegills and if i'm catching tons of crappie ill keep 7inchers... bluegills are mainly stunnted b/c of the predator to hiding areas ratio.(EX.) if there are 50 bass in a less than 1 acre pond with little hiding area the bluegills will be big b/c they will hav 2 be sneaky 2 avoid the bass. (Greensunfish never get big anyway)