Originally Answered: is garlic infused fish food good for the fish? 10 points to best answer?
There seems to be a fair amount of evidence that garlic or at least the addition to the fish food of a 3% portion (quite a bit) will inhibit the spread and of even presence of parasites and harmful bacteria within fish studied. They also had a lower mortality rate than control groups (fish treated the same way, but without a garlic content in their diet.) At least one commentator suggested that the garlic content must be relatively considerable and not a trace quantity of garlic or the chemical allicin in their food.
On a forum elsewhere (the late and lamented guppylog) I was dismayed by the number of cases of Cammalanus that seemed to show up a from a few days to three months after purchasing new fish. Quarantine, without treating with for broad spectrum of parasites while the fish is in quarantine (which darn few places do) is useless against those nasty intestine-gnawing bloodsuckers.
Because of the damage wrought by these worms, by the time they are discovered, it is almost too late to save the stricken fish, though treatment of the whole tank with the anthelmintic (anti-helminth or anti-worm) chemical Levamisole or the less expensive Flubendazole is worth it to save tank mates and fry.
On guppylog, almost more discussions on "Camallanus/Worms/Red "strings" coming from anus" were saved than on any other topic
Being able to feed all of one's fish with a garlic added food is a terrific way to head off the very contagious Camallanus. And it is cost-effective.
I looked at the ingredients of the 4 or 5 flakes I rotate in the fish room. At the moment, only the veggie flakes don't have garlic, which by the way seems to also be a taste attractant. It is also to the manufacturer's advantage to include it because often the fish take the flakes enthusiastically.
The only flake I can give our dog (inclined to follow me around and beg) is one of those veggie flakes. Onions and garlic are very bad for dogs too. They will show no harm and suddenly, even after years, because something accumulated, they will get very sick or even die painfully. (And look at all the prepared meals for people where meats have garlic in them.)
As a few of you may have noticed, taking garlic supplements has become more popular with humans. That second study mentioned below concluded that "it can be suggested that adding 3% Allium sativum to fish diet can promote growth, reduce total bacteria, and improve fish health."
Some of the same things claimed for humans, a more efficient immune system, more efficient digestion, a more efficient liver = the ability to remove more harmful things from the blood, can be claimed for the fish.
Another great reason to use garlic is that commercial fish farmers (both for food fish and ornamental fish) have been adding antibiotics to their food. That scatter-shot approach hasn't been as effective in keeping the fish healthy as using the garlic extract. Also, and this is increasingly important, we aren't helping lots of pathogens to become resistant to antibiotics. That way if antibiotic help is needed, but rarely, "they" will not have to come up with new antibiotics at such a frenetic pace.