It is obvious what happened.
The two of them got wrapped up in the heat of the moment. Their energies were feeding off of each other. And before they knew it, they had murdered an innocent fish.
They were shocked at what they had just done. Could it really be possible? Were they really monsters? Or were they just two excitable fish, swept away in the spur of the moment bloodlust in which they found themselves, uncontrollably, wrapped up.
They couldn't even look each other in the eyes. They knew what they had done, but couldn't confront it. So they went their separate ways, to their caves, to deal with their agony alone. The guilt from what they had done continued to eat away at them from the inside out. They were consumed by these feelings of sorrow. Oh, what ever could possess them to dispatch of their damsel comrade in such a way?!?!
Unable to eat, unable to move, paralyzed by the fear, guilt and sadness, the two damsels remained, alone, terrified of who they had become.