There's a guy in Myrtle Beach that will sell you all equipment for turtles, but will tell you repeatedly that it's illegal for him to sell you one less than 4" long. Wave enough money under his nose, and he'll sell them to you "under the table," or out the back door. He knows the law, but he also knows how to get around it. I know this, because I have two that came from him. They were given to me by a guy that bought them for his kids, but the kids' interest waned and he got tired of cleaning up their tank. I've had them 4 or 5 years (don't remember exactly), they have grown from about 2" long to around 6" now. I recently switched them from a growth formula pellet to a maintenence formula, since their dietary needs do change as they grow.
