oh okay. Let me explain, Shimmy (in this definition) is a disease that freshwater fish can get that makes them move as if they were swimming, but they never actually go anywhere. Fish that give live birth, such as mollies and guppies, get it quite often. I wasn't suggesting that your dats have shimmy, just trying to figure out the motion. But if it is just their pectoral fins, that is normal. As your dats grow, they will need a much larger tank though.