Sorry if this has already been posted - I'm having problems trying to work out out to post a query!
I am new to the whole marine thing and bought a tank with sump etc a few weeks ago - a week ago I added live rock from Fiji and Indonesia and last night I noticed a mantis shrimp poking his head out of a hole in a piece of my live rock. He's very small (approx 1cm in length) and brown mottled with iridescent blue streaks - I think it might be a Gonodactylellus caldwelli or Haptosquilla trispinosa - which hopefully it seems won't grow too big. The problem is I was hoping for a peaceful little tank (48inch x 15inch x 18 inch) with clowns, gobies and blennies plus hermits and shrimps and corals. However, I am worried the mantis shrimp might cause me problems. My lfs has advised me to get rid of him, however, he's a nice little chap and I quite like him. If I feed him enough will he still attack any fish/inverts I add to my tank? At the moment it's too small to be a problem, but I'm not sure how quickly he will grow and become a menace... If necessary I could get a nano tank for him but at the moment I don't have the budget considering I've only just bought my new aquarium... any advice will be appreciated!

if it were me id look at re housing or talk to LFS to see if anyone wants him, some people like them some people hate them, as to if he will still kill fish, most likely once he gets hungry he will and unfortunately you cant guarantee he will get enough of the food you out in there to keep him going, all in all it should be kept in a species tank. worst case scenario you may have to take matters into your own hands, having said that do all you can to rehouse him first, as killing anything really isnt great.

i used to have a mantis shrimp in my tank which had housed itself in a piece of live rock with soft polyp mushrooms on, the quickest method that i was advised was to simply remove the rock and pour sparkling water over it, flushing the shrimp out (into a bucket). The mushrooms survived fine and are now thriving - without a mantis under them!!

If he's that small, I can't imagine it catching a fish anytime soon, and most snails are probably too big as well...