I have a community 200 liter tank with your average grouping of swordtails and neons. Well, I was headed out to the pet store for a few things and the wife decided that she wanted to go along. She saw her first fiddler crab and bought him to put into my tank. I let her put him in there under one condition: "If he harms one fish he's gone". Well, he's now the center of attraction of the tank! He loves to get on top of my driftwood, and peek over the large clump of Java Moss, and while he's there he waves around his one big white claw. Upon seeing this "waving" we watched the tank closely to see what he was doing. He wasn't trying to catch the other fish, but from the looks of what was going on, he looked like a traffic cop directing traffic! The fish almost seemed to be following his directions. He is now named TC for Traffic Cop and when my friends come over that's the first thing they look for. He does it all the time.