This will be interesting to see. I've never heard of them eating fish of any kind, and apparently they aren't very prolific (I've been seeing them imported for several years, and haven't found anyone in the US that had extras to sell me). As far as overrunning the tank, I was on a waiting list (waiting for imports to arrive) for over two months trying to buy them at $6 a piece...that's exactly the kind of overrun I'd like to have in my tanks! Aquabid, here I come.