Yep... they'll try to eat anything that will fit in their mouths. Besides, they like the water to be cooler so they aren't suitable for a tropical setup.
Also: fish will pick at the 'fluffy' gills and, the water needs to be as deap as they are long in order for them to take gulps of air every now and then!
yes! the fish will get eaten and/or severly wounded, even if they are large.