I had the same thing happen with gold fish in my turtle tank...Bought 8 tiny ones for the Maps and Stinkpot and months later I had 8 large gold fish in the tank with them. They went back to the lfs. These turtles are about 7-8 months old and have never eaten or gone after a fish. I watched them with a flashlight at night several times and when the goldies were sleeping the turtles would just walk into them over them etc.