Here is my story with blue lobsters.
I was at my LFS two three ago and i saw one, quite big. I knew i wanted it but i couldnt have it as they had a note saying that is is reserved.
I went to a different store and found one smaller and i bought it. I know people usually say dont mix them with fish but i put it in a tank with mollies, guppies, gouramis, angels even low feeding fish like clown loaches. Its been three weeks and i havent lost a single fish. (Yet).
Im just waiting to see if i start loosing fish then ill put it in a separate tank but so far all is good.
All it seems to do is just hide and it only comes out when i feed the fish. I give it muscles but for some reason it seems to prefer cat fish pellets..
Will keep you posted..