Hurt Clown Fish

Alright,
     So today my male Clown Fish, Marlin, was acting weird all day long and I couldn't see anything wrong with him. Later into the day I started to get worried about him so I did a 5 gallon water change to bring dissolved chemical levels down. It helped a little, but then he went back to the same way he was before. Just kinda hovering under an arch in the aquarium.
     At a closer look, his right gill was swollen! How could this happen!?!?! I and my partner came to the conclusion that he had been chasing the black and white damsels around the rocks and hurt himself. We removed the damsels, and believe me that was a good chase around the tank lol. Now the damsels are all alone in the 80g aquarium and we are going to use them to cycle the new 80g aquarium and then we are giving them back to the pet store. They are too aggressive and now the male clown fish, from a mated pair from the wild, it hurt and is on the verge of dying.
     It is now 11:35pm and all the lights are out and he seems to be resting up fine, but we should know by the morning if he is going to make it or not. His gill is pretty swollen, but seems to be breathing fine, but who knows. This is a learning experience and we are still learning as we go.
ONE THING FOR SURE, WE WILL NOT BE PURCHASING DAMSELS AGAIN!