The picture really isn't clear enough to see what it is.
I had a rainbow fish with a bump/tumor/growth that surrounded the attachment of his pectoral fin. He lived quite a few years and died an old fish. I don't think the growth affected him much. I also don't think it had anything to do with his death.
Sorry, I can't tell what's going on with your loach. If he's acting normally, at least that is a good sign.
wren