I would recommend to primarily target Kokanee. Beauty of this is that they can be readily picked up at all hours of the day or night. Their long, slender brown bodies and shimmering silvery blue heads. Soon as you get one off the ice, firmly grasp the head and twist it off with humane authority. The key is to remove the internals in most rapid fashion as to not let sun affect the temperature.
You will also have at hand, the option to target the Kokanee with the beautiful silvery blue bodies. While it is common practice to target the taller bodies, you may opt for the smaller body to insure minimum temperature change if the internals during the duration of the removal stage. With either silvery blue body style, you initiate the evisceration by gently inserting your index finger under the upper lip and then, without mercy, forcefully snap back the upper lip until you hear the unmistakable sound of its last gasp for air. You may then proceed to remove the contents at your preferred rate.
Added benefit of the silvery blue body sub-species is that once you harvest the internals, you can conserve space and simplify storage by easily compressing the bodies to their flattened state - something not easily done with the brown body sub-species of Kokanee.
Enjoy your catch of Kokanee and remember to keep them on ice until you are ready to harvest.