Interesting little guy. What type of prawn is he and where did you get him? I have always been interested in prawns because they are so closely related to FW shrimp, but the fact that they eat your fish is a problem. I have seen pictures of brackish prawns that have thin claws 3 times the length of their bodies in Tropical Fish Hobbyist Magazine. The thing couldn't even hold it's claws up when it was out of water! It would be cool as heck to have a couple of those in a species tank, though. Your friends could all come check it out and talk about how they would like to fry it up and eat it.
Two 1 GA desktops, a 5 gallon, a 2.5 gallon, a 10 gallon, a 20 gallon, a 25 gallon, and two 75 gallon tanks, all planted.
I am an expert on algae, so ask me if you have questions. I know how to grow it, just not how to get rid of it.