This time of year, I ice them as soon as I catch them. The cold slows down their motabolism which restricts the blood flow and keeps the blood out of the meat.
When tournament fishing this time of year (walleye) we have to keep them alive. Obviously, the livewell is the way to go but, we keep the water as cool as possible by tossing in frozen 20oz soda bottles when needed. I also pull the plug and cycle the water out regularly.
I've never gilled a fish on purpose in my life. Whether it was running salmon charters, fishing for walleyes, or crappies, perch etc. The key this time of year is to decide right away if you want to keep them (on an all day trip). If so, send them in the ice.
A trick I learned from another member of crappie dot com: He is an offshore fisherman (does it for a living). He actually mixes his ice with salt. Almost like an ice bath with water. For whatever reason, the salt and the ice keep the water colder and the ice lasts longer.