HI,
Do you notice any other sympotms? Like breathing heavily or ??
IMO, it looks like brooke and you need to move qucikly to help him.
A formalin dip is the way to treat this parasite.
remeber to watch him closly for any signs of stress in the dip.
You need to take him out of the main tank and use a bucket for the formalin and then a QT tank after the dip then when he is healthy go back into the main tank.
Dont dip then put back into the main.