My wrasse is around 9 years old. I know lifespans vary on species but im not sure of his species. He's yellow on the top, kinda greyish black on the bottom with blue lines near his eyes. So he was eating clams and swimming around and doing fine and suddenly after coming home from school, dead in the back of the tank. Water quality was fantastic, everything was fine. Is this just of natural causes? He had no infections, viruses, etc.