The best for this situation is trial & err.
Also known as experience.It is some times real hard to determine whether to bonk or not to bonk a darker shade of hatchery fish.
Getting caught up in the moment is hard to stay away from.If the fish is leaking or singaling eggs release it,if the fish is milking release it.If the fish has already done it's thing release it.Other then that look for the belly to be light grey towhite for best quality.Good luck,
STRIKE ZONE