if they are slender enough to fit in his mouth then maybe 3-4" for his length. If they are as tall as they are long ie discuss then when his head is 3-4" wide, but he still might try before then and either get them stuck in his mouth or just pummle them to death. For the rtc's sake I wouldn't put anything that looks like he might concievably be able to fit into his mouth in the tank with him. It could get stuck and kill him. I've seen it many times on here before. Good luck.