With trout season on the way, a useful chart. ("Exercised" means you played the fish a bit before netting):
Event, Seconds out of Water, and Survival Rate
Fish caught, exercised but not taken out of water 0 secs. 88%
Fish caught, exercised and taken out of the water 30 62%
Fish caught, exercised and taken out of the water 60 28%
Fish caught, exercised, placed in boat, handled and flops around
60+ 0%