Yer friends tank is probably gonna implode soon. See, people dont understand it isnt size, it is the biological output. They seem small, but the amount of food that they consume and then transfer as waste back into the envronment is harmful. A russels lion is NOT small, and a full grown one, although smaller than a volitan, is still too big to be kept in a 55 gallon with any other tank mates, and like i said, id feel uncomfortable keeping a russels in a 55. It isnt very wide, and they will feel cramped wen they spread their fins out. So, if u REALLY need a russels, and only have a 55 gallon, then it should just be that one fish, or else u can get a dwarf lion and an eel and something else, and be pushing it with that combo.