I have three Columbian Sharks in my 55 gallon brackish. They are about 4-5 inches each. They eat a LOT! I alternate feeding them sinking shrimp pellets, freeze-dried bloodworms, and frozen brine shrimp (which they LOVE). I also have a needle nose gar in the same tank that I feed live feeder guppies. The sharks are amazing to watch. They move all shark-like along the bottom of the tank, looking for food. I'm waiting for them to get bigger so they'll start eating live feeders also, then the entire tank will eat the same thing. Will still alternate food with the sharks though.