Whatever you do dont keep it with a bass!!!! Pickerel are stalk eaters and follow it around for awhile and then ambush it. As you very well know bass destroy the first thing that comes into the tank. Pickerel dont even do good wuith bluegill. Bluegill and other sunfish mistake the pickerels fins as food and eventually will take huge chunks out of the pickerels fins. Red fins are probably best by them selves and as they only get about 10in long you might be able to even do two in 55g. But again they need vegetation and hiding spots. Pickerels act almost like trout in the wild, they are found in wild streams and hang out in pools where there is good cover and spoke very easily.