Yes, garlic is not only a natural "warder offer"

D) of internal parasites, but a documented appetite enhancer. It can coax even sick fish to eat that otherwise may not.
Relatedly, when you go deep sea fishing, it is not uncommon for people to dip the chum in garlic juice or the commercial "garlic substitute", or even string whole cloves onto their hooks. It gets the fish biting.
There is a chemical in garlic that causes this. Let me look for the name because I can't remember it offhand.
EDIT: The chemical substance in garlic that is linked to appetite is called allicin. There may be more, but that's the one I was thinking of. A google search furnishes all sorts of things on it - it boosts lung health in rats for instance!
"Garlic will stimulate appetite and metabolism, clear toxins, and act as an antimicrobial agent of the mucous membranes. A great deal of recent work has been done on the sulphur bearing amino acids in Garlic"
http://www24.netrition.com/garlic_page.html
(admittedly that's not a really scientific site, but the info is pretty much the same).