Can you use a turkey baster to put food right in front of it to get it eating? If not, I'd say it's a judgement call on your part. If it's really struggling and in pain, you should probably end it. Poor little fish!
had fish for probably one year disappeared for a whil about month ago and reappeared a week later bomping into things now he just hangs out vertical in corner he is eating but not much always missing food :sad:
and anthias need to eat small amounts frequently for optimum health...thats gonna take some dedication to keep him going...good luck with whatever you decide