I can't see any sign of biting nor much of necrosis that caused the problem, judging by the sheer fin volume he has either snagged himself on something or it is a blowout.
This will heal itself over time but you can help by adding some AQ salt or an indian almond leaf to his tank to speed healing and keep down the chance of infection and perhaps bolster his diet with something protein rich like bloodworms very few days (frozen or live are best).
He should begin knitting that fin up in no time
This will heal itself over time but you can help by adding some AQ salt or an indian almond leaf to his tank to speed healing and keep down the chance of infection and perhaps bolster his diet with something protein rich like bloodworms very few days (frozen or live are best).
He should begin knitting that fin up in no time
