I have a 20H (24"x12"x16") with a stock of 2 yellow perch (both 2"), 5 Johhny darters (2"-2.5"), and 5 blacknose dace (four are 1.25" and one is 2"). Believe it or not the 2" dace is actually bullying everything in the tank including the perch which I find ironic since the perch would eat them like candy when they get bigger. I've never even heard of dace attacking other fish, especially benthic rhinichthys dace so I'm not sure whether I should ignore it considering Rhinichthys species can't do much as far as nipping with their small down turned mouth or separate the aggressive one from the others.