As TJ alluded to, yellow perch are a favorite of largemouth. I see people stock them in ponds around here and they never see them again. You'd have to have a ton of vegetation year round for them to have a chance. I honestly don't think algae would cut it, as it'll come and go throughout the year, occasionally leaving them vulnerable. If you're pleased with the condition of your bluegill, and if that is your goal, I'd stick with that. Tempting to add a species you enjoy, but wouldn't mess up a good thing. If the yellow perch do establish themselves, they'll compete with your bluegill, though they are more predatory, so a slightly different niche.
