I voted for mixing with fish as I have kept C. Orientalis with White Cloud mountain minnows, however when they started aggressively swimming at the newt, I gave them to a colleague at work. The place where I got my newts from had C. orientalis, T. Marmoratus and Notos, all in one tank with goldfish. I bought 2 of the C. Orientalis and 1 Noto (the marbled newts looked on deaths door so I left them) I kept them seperately in a 14 litre tank each, however the Noto crawled out of the water on to the top of the filter and refused food till it died 2 weeks later. Like an idiot I went back to the shop and bought 2 more, but pretty much the same thing happened, despite me removing the filter, changing the water like mad, and keeping an eagle eye on them. I reckon it was, at least partially down to them being kept the way they were in the shop. My C. Orientalis are doing well though, I have to say.