Good to hear you have a redfin pickerel, I breed them from time to time in my ponds. They are great fish and if presented with appropriate live food do well. I wouldn't count on it eating anything dead. I raise tiny ones of daphnia magna and then to baby gambusia. a three inch pickerel should be able to eat small guppies. Around here (SENC) they feed almost exclusively on gambsia, although I am sure they will eat anything small enough to swallow. 78 degrees is fine for redfins, I catch them all the time in water in the mid 80s. My ponds get into the mid 80s in the summer as well. The only reason they might need cool water is to induce them to spawn. They are one of my fav native fishes, if you need any more info let me know. Be very careful about your tank cover, they are jumpers and will jump out of they get the chance.