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Hardware components of my two primary tanks and some of the fish I keep
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Garlic is bad for fish Part II - from Humaguy

Posted 02/27/2014 at 03:50 PM by snorvich
Updated 03/18/2014 at 05:36 PM by snorvich

Garlic must assuredly be a proven method of disease treatment. Why else would so many reputable manufacturers make and market a cure if it had not been scientifically proven?

Taking these points in order, first garlic has never been conclusively proven to cure Marine Ich (Cryptocaryon irritans), ever. Some hobbyists have used it and reported that their fish got better, but these are not controlled studies and none of these hobbyists know for certain if their fish's own natural immunity was the true reason for the cure, or if garlic had any impact whatsoever. Also, there are a number of hobbyists which have used garlic and suffered significant losses of fish as well.

Second, quarantine tanks are a cost-effective and simple method to ensure the health and well being of your aquatic pets. These tanks really should be standard in this hobby and it is a real shame that they are so often overlooked. In my opinion, stores and fellow, experienced hobbyists who don't recommend this protocol to beginners are doing them and the hobby in general a disservice. Advocating that aquarists play it fast and loose when it comes to quarantine is frankly irresponsible and is likely setting them up for eventual failure.

Third, while many hobbyists report using garlic and then noticing an increase in feeding activity, there is no conclusive proof to this claim, either. It could be that the pungent and/or unrecognized/unnatural smell of the garlic brought the fish over to investigate the food, but there is no way of knowing whether or not they would have eaten food not treated with garlic, or whether or not any strong-smelling food additive would have done the same thing. It could also simply be that enough time had elapsed that the fish was finally prepared to eat and adding garlic was just a coincidence. Frankly, there are far too many variables to conclusively evaluate these claims.

And regarding the last point above, so many manufacturers are making these products because there is market demand for them, plain and simple. A lot of people are buying garlic-based medications, so the manufacturers are simply giving the buying public what it wants. The list of manufacturers that have jumped onto this bandwagon is truly impressive. Just about every major manufacturer is marketing its own brand of garlic extract. A quick search of a couple of my local fish stores yielded the following:



People describe garlic in a number of different ways. The most common is simply to say they treated the food with garlic or garlic extract. Those are both easy enough to understand. But, various references also use other names. The scientific name for the garlic plant is Allium sativum, so don't be confused if that name comes up when reading other articles or any of the references listed at the end of this article. Some people also use the term allicin. That is shorthand for the active ingredient in garlic extract. Chemically, allicin is diallyl thiosulfiniate or diallyl disulphide-oxide (Cortes-Jorge 2000). All of these terms, though, are generally talking about the same thing.

Garlic as an Appetite Stimulant:



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I was able to find one brief report from the public aquarium literature that attempted to use garlic extract as an appetite stimulant (Ashdown & Violetta, 2004). This "experiment" was conducted at SeaWorld in Orlando, Florida. A 660,000-gallon display containing 50 assorted elasmobranchs was the test tank. It held 19 sand tiger sharks (Carcharias taurus). Of those 19, two of the sharks had refused to eat regularly and had begun to lose weight over time. Sand tiger A once weighed in at 108 kg in 1990, but by April 2003 was down to 73 kg. Sand tiger B was its largest in March of 2002, weighing 74.5 kg, but had also decreased in size and weighed only 70.6 kg in April of 2003.

At that point, each shark's food received garlic added in the ratio of 1 cc of minced garlic per pound of food offered. They were then fed the garlic-laced food for 13 weeks. Sand tiger A took to the treated food immediately with new vigor. It ate near or above its targeted allotment of food every day during the testing but one. And on that day, the shark had been weighed, so the SeaWorld personnel felt it was possible that the stress of the procedure affected its appetite. But, sand tiger B did not demonstrate the same change in behavior. It refused to eat at all for the entire first month of the testing phase. And when it did finally eat some of the garlic injected food, its feeding behavior did not improve and it continued to feed only sporadically.

All in all, this brief report is certainly not a ringing endorsement of garlic as an appetite stimulant. That said, there are numerous problems with this study. First, from our perspective as aquarists, they made this attempt with sharks and not standard aquarium fishes. Second, they used only two test subjects. A larger group of fish would be best for comparison. And finally, there were no controls to speak of. Since we cannot discount some other factor having been involved in sand tiger A's behavioral changes, we really can't draw any conclusions from this report.

This brings me to my real point, which is that this highly flawed study is no better or worse than someone saying, "My fish would not eat. Then I added garlic extract to their food and they now eat great!" These reports are practically meaningless. Just as we cannot draw any conclusions from this public aquarium trial, nor can we draw any conclusions from similar unfounded statements made online.

Garlic Versus Mycobacterium marinum:



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Garlic has been studied for its effectiveness against a bacterial infection of fish (Colorni et al, 1998). One hundred and sixty sea bass (Dicentrarchus labrax) were intentionally infected with Mycobacterium marinum via injection with cultured cells. The study's participants also kept a positive control group of another 40 specimens, which they held in conditions similar to, but separate from, the infected fish, but injected them only with saline. All of these fish were then held and monitored to watch the disease's progression. After nine weeks, the infected fish showed clinical signs of infection upon dissection and examination. At this point, the infected fish were broken up into four smaller groups of 40 each: a negative control group which received no treatment, an experimental group that received antibiotic (streptomycin) injections, a second experimental group that received garlic extract injections, and a third experimental group that received injections of both the antibiotic and garlic extract. All fish were treated for an additional 12 weeks. During this time, sample fish were selected and dissected to monitor the disease's progression or recession.

The interesting revelation that came from this study is that it revealed a statistically significant stronger immune response in the fish given only garlic versus the fish given antibiotics, antibiotics and garlic, or the untreated control group. Part of this apparent anomaly is that antibiotics also have an immunosuppressive effect. In layman's terms, while they work to kill bacteria, they also don't permit the body to fight as hard as normal against the infection. But, the fact that the fish treated with garlic showed a stronger immune response than the untreated control group lead the study authors to suggest that "allicin treatment seems to have an enhancing effect on antibody activity when compared with all other groups."


A Heniochus butterflyfish in a reef display with the tell-tale spots of a marine Ich (Cryptocaryon irritans) infestation. Because of the perceived difficulty in removing sick fish and because so few hobbyists follow quarantine protocols, a lot of aquarists are 'experimenting' with garlic and keeping their fingers crossed.

The bad news is that this paper dealt with a bacterial infection. There is no relationship between garlic's effect on bacterial infections and parasitic infestations. Also, the fish were not fed garlic-laced food; they were injected with garlic extract. That brings into question whether feeding fish garlic extract would be as effective as injecting them with it. Additionally, the garlic extract was prepared freshly for every injection. This is particularly important when taking into account the effectiveness of commercial preparation, and also in light of the fact that allicin, the active ingredient in garlic, is unstable and prone to breakdown in a relatively short amount of time (Cortes-Jorge 2000). Furthermore, since garlic is a non-natural food, the antigen effect of a novel compound may have been responsible for increased immune response, and although they used a negative control (nothing), they did not use a similar variable - i.e. onion, paprika, nutmeg, or whatever else one has in their spice cabinet that they think might somehow help their fish fight disease). And finally, even though all the fish showed improvement by the end of the study, none of the fish was completely healed. They all remained infected with Mycobacterium marinum, although at low levels.
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