Australasian Science: Australia's authority on science since 1938

Garlic Deters Bloodsuckers

By Stephen Luntz

Garlic can protect fish from parasites.

Medieval peasants who clutched garlic to deter vampires were not entirely wrong: regular doses of garlic can indeed protect against parasites, at least if you are a barramundi.

“For Australian fish farmers, one particular flatworm parasite, Neobenedenia spp., has caused substantial financial loss and headache in recent years, but until now there has been limited success in developing a successful treatment for this parasite,” says Thane Militz, a PhD student at James Cook University’s Marine Parasitology Laboratory.

“Previous research has demonstrated that feeding fish garlic significantly improves their immune system, and we wanted to take this research a step further to examine if there was any medicinal effect against parasites,” Militz explained.

“The breakthrough was discovering that barramundi fed a garlic-enriched diet showed considerably more resistance to the problematic flatworm parasite compared with fish reared on a traditional diet.”

Militz says that garlic’s popularity as a herbal remedy in Asia drove research on its use to improve immunity in aquaculture, and he decided to follow this up by testing the effects on the damaging worm.

An unexpected benefit of the trial was that the fish fed pellets infused with 10–30 g/kg of garlic ate more, which may lead to faster growth.

The barramundi were exposed to parasites after a period of either 10 or 30 days on a garlic or control diet. While 10 days of garlic produced minor benefits well within the margin for error, Militz reported in Aquaculture that only half those fish that had a whole month of building up their reserves became infected, compared with all of the control group.

The two doses appeared equally effective, and Militz estimates the cost will be just 5¢ per kilogram of feed, or around 3% of the current price. Garlic has a high affinity for the lipids in fish feed, so little of it leached into the surrounding water.

So far there is no confirmation that the benefits extend to other species of fish.

Militz says he would have liked to test if the garlic diet had any effect on the taste of the fish but adds: “Sadly my ethics clearance would not allow me to eat my subjects”. However, he doubts the effect would be large as most of the chemicals pass through quickly.