I have a brown and a green FBT and have had them for a few weeks now. Today I noticed that the green one keeps grabbing the brown one and the brown one sometimes tries to fight him off and ends up on his back with the green one on top. Most of the time the brown one just sits there, or puts up a mild fight and give up, and the green one is holding on to it and kicking his back legs. It happens in the water and on land. Are they fighting or mating and if its fighting should I separate them?