I would be concerned he caught something viral from the fight he was in and to esablish what it was and to treat it will require a trip to the vet. Respiratory issues can get bad very quickly so getting him on antibiotics quickly is the key to a speedy recovery. I know you are having money issues but the longer you wait to take him in, the worse it will get and the more it will cost to get him healed.
Let me know if you have any other questions
Good Luck &
Best Fishes
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