I have a common Pl*co in my 20 tank and he is still young and only about 4 inches. However he does something strange, when he is out and about in the tank, he sometimes darts up to the top of the tank, spews bubbles or something and darts back to the bottom with a few airbubbles coming forth from him? Does anyone know what he is does or why he does that, is my Pl*co the only one to do this? thanks