I have kept mottleds but not slimies, the slimy requires colder water but the mottled will adapt to an unheated tank if it has lots of warter flow and a high O2 level, mostly they prefer conditions similar to trout. The mottled can get to 6" and the slimy to 4 1/2", both are very aggressive feeders that will eat fish at least 1/2 thier size, They are very movement oriented and I have caught 2 1/2" ones on silver spoons that had a total length of 3", they eat insects, worms, other inverts, and fish and fish eggs.