This will be my first year to hike Whitney so what I'm about to say is biased on my research, not personal experience. I've heard that Consultation Lake holds some decent sized rainbows. At the moment it appears to be frozen over. Mirror Lake looks like a hidden gem, It should have some nice brooks. Don't forget about the extra bounty on brooks this year (if you don't catch and release). If you do not know if this site already you will want to check it out:
DFG USFS fishing guide 
