also, not all the shrimp you collect will be peppermint shrimp. there are a ton of variations found in nature and you may end up with something that isn't safe for your tank. please don't bring any fish back with you unless you know exactly what it is. you'd be surprised at how many "small" fish end up over a foot or two in length.
if you do get something you don't want...either destroy it or find someone who wants it. do no release that animal back into the wild after it has been in your tank or in any water that came from your tank.