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