Been wondering that myself... What is crazy is that he is breathing good and follows you with his eyes when you move ,so it makes it hard to watch. My other Arowana keeps getting close to him like she knows he is injured and wants to stay close to him. In the past month they have started to act like they were wanting to mate and now this happens. My 2 Fire eels have stayed in the corner and they never do that. I have had Arowanas for the past 25 yrs and I have never seen anything like this.