15 gal they were paired before I got
Tail is bitten, a sign of aggression. Additionally clown is thin and is likely a victim of aggression and cant see remainder of body to tell if any other injuries. Isolation will give this fish best chance for recovery.
It’s the bigger one of the pair though and no other fish are in the tank ?
Thats correct. The bigger one is often the female and is a result of clownfish hierarchy where the female clownfish are much more dominant than the males. They become greedy and try to eat most of the food that enters the tank (which is one reason the males don't grow as large). They often become aggressive to protect their home which may be an anemone, a nesting area, or the entire tank. If it attacks your hand when you're trying to clean the glass or it won't let any other fish near its zone, you likely have a female clown. Often if you separate the female for a week or two into an acclimation box or sump, there may be a change in her behavior, and you will quickly see the male come out in the open
