that's horrendous...
i once had a pair off piranha when i was younger around 6 inch, one ate the others head half circle just above the eye to the dorsal, looked like i had a bit if you knnow what i mean, that pirahna lived like that for two weeks!
had an 7inch oscar jump before while maintanence happened, hit the ceiling then layed on the floor motionless thought it was dead, put it back in the tank and within 10sec it woke up,,, knocked out i guess lol lived for years!