If all a new hobbyist were to do was gloss over the medicine aisle at his favorite local fish store and observe the proliferation of garlic-based treatments, or peruse the various online postings of garlic's proponents, he would surely come away with several likely impressions:

• Marine Ich/Cryptocaryon irritans (and just about anything else) is easily cured by feeding garlic.

• Quarantine tanks are an unnecessary expense and hassle (assuming he has even heard of a quarantine tank).

• Garlic is a proven appetite stimulant, which can compel even challenging-to-feed fish to take prepared foods.

• 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:

Ecosystem Garlic Elixir
Kent Garlic X-treme
Seachem Garlic Guard

Various brands of fish food are now even promoting that they have added garlic to their recipes. And yet, none of these alleged benefits has ever been proven. That is not to say that no studies have been done on garlic and its use to combat fish diseases. Several studies have been published regarding garlic, but none of these has dealt with Cryptocaryon irritans, which seems to be the most common ailment for which garlic's use is advocated, likely because it is simply the marine ornamental disease most commonly encountered.

Garlic by Any Other Name Still Smells Just as Pungent:

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:

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:

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."

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.

I wonder if this could this be why some people who don't use conventional, proven treatments such as hyposalinity and copper see repeated outbreaks when adding new fish or when their current fish become stressed? The idea that garlic could possibly help with a stronger immune response but not completely eliminate the pathogen is intriguing to me. This would help to explain some of the posts on the internet message boards of repeated outbreaks as well as provide false evidence to the believers that Marine Ich/Cryptocaryon irritans is always present. That theory aside, I have already stated that bacteria are completely different than parasitic protozoans. There maybe no correlation at all. It is simply something that struck me in my reading.

There is also one more problem with this study. When they began, they believed that they had naïve fish, ones that had never been exposed to Mycobacterium marinum. But, as the study progressed and additional tests were undertaken, they later believed that the fish had had some previous exposure to this pathogen because of antibody counts in the unexposed control group.

Sodium Percarbonate and Garlic Versus Ichthyophthirius multifiliis:

One interesting paper (Buchmann, Jensen, & Kruse, 2003) detailed work done with sodium percarbonate and garlic extract against Freshwater Ich/Ichthyophthirius multifiliis. The push for this study involved malachite green, a substance routinely used to deal with this parasite that was banned for use on food fish because it is carcinogenic. So, safe yet effective alternatives were being investigated.

This study was strictly an in vitro trial. Basically, parasites were harvested, placed into Petri dishes, exposed to sodium percarbonate or garlic extract, and then monitored to determine the lethal concentrations and exposure times of both. The study found that sodium percarbonate killed the free-swimming infective stage of Freshwater Ich/Ichthyophthirius multifiliis at 12.5 mg/L for 180 minutes or 62.5 mg/L for 90 minutes. Garlic extract required 62.5 mg/L for 900 minutes or 312.5 mg/L for 180 minutes to be effective. For comparison, malachite green is effective in 90 minutes at only 0.5 mg/L or 900 minutes at 0.1 mg/L, much lower concentrations than either of the experimental treatments. For the parasite's reproductive cyst stage, no concentration of sodium percarbonate was noted that differed from the control in effectiveness, while it required 570 mg/L of garlic extract to kill 100% of the cysts. Again, for comparison, only 0.15 mg/L of malachite green is needed to kill 100% of the cysts.

That all said, like the other two experiments I discussed, there is little that we can conclude from this paper, either. First and foremost, Freshwater Ich/Ichthyophthirius multifiliis and Marine Ich/Cryptocaryon irritans are not very closely related (Colorni & Burgess, 1997). While it is obvious to anyone familiar with scientific names that these two parasites are in different genera, they are also in totally different classes, with Freshwater Ich/Ichthyophthirius multifiliis being in Oligohymenophora, order Hymenostomatida and Marine Ich/Cryptocaryon irritans placed in Colpodea, order Colpodea. While these two ectoparasites share an apparently similar lifecycle and dispersal mechanism, these similarities are likely caused by convergent evolution rather than by having evolved from a close common ancestor.

As further evidence of the difference between these two parasites, note that malachite green, the medication that the researchers were seeking to replace, is very effective against Freshwater Ich, Ichthyophthirius multifiliis, but is generally not recommended for use against Marine Ich, Cryptocaryon irritans. So whether or not garlic is ever proven to be effective against Freshwater Ich, it does not automatically follow that it will be equally effective against Marine Ich. In fact, there is no a priori reason at all to expect that any medication effective against one of these parasites would also be effective against the other.

Second, this study was only the first step with in vitro experiments. These drugs were not tested on affected fish. It could be that these drugs at these concentrations do work against the parasites, but could also be deadly to the fish. For example, other experiments on saltwater fish infected with Marine Velvet, Amyloodinium ocellatum, showed that hydrogen peroxide was effective in ridding the fish of the parasites, but it also induced mortality rates of anywhere between 30% and 100%, depending on the amount used and the subject being tested (Montgomery-Brock et al, 2001 and here). Clearly, this illustrates the importance of finding a treatment that works against the target organism but doesn't endanger the host fish.

Now, I understand that many are going to argue that garlic is natural, so regardless of its concentration, it should be safe. My response is simple: palytoxin is natural as well. So is lionfish venom. A lot of naturally occurring substances are harmful, even deadly. Just because something is natural does not automatically render it safe.

Finally, because this was an in vitro trial, the garlic extract was not fed to the fish, as there were no fish to feed. The extract was simply added to the water and it was noted whether or not it had an effect on the parasite's cyst or free-swimming stages. This raises yet another question of whether or not garlic extract in food would be effective at all.

Garlic Versus Intestinal Worms:

One article (Fairfield, 1996) that I found details an experiment conducted using garlic extract to combat a nematode (Capillaria species) infestation in common freshwater angelfish (Pterophyllum scalare). The author of this article went to various breeders, wholesalers and retailers looking for angelfish in which this worm was present. Suspected host fish were given a colonic wash to look for evidence of worms and/or their eggs. From a wholesaler, sixty individuals were selected for this study that were described as having a "moderate to heavy load of these parasites." These 60 fish were divided into two groups. From each group, five individuals were randomly selected, killed and dissected to examine the number of worms and eggs present. An average of 2.1 worms per fish was found in the dissected fish along with an average of 10.3 eggs per fish. The remaining 25 fish from each group were given another colonic wash. The author found that these fish had an average of five eggs per fish, but no worms were extracted during the colonic wash procedure. Both fish groups were housed in identical 55-gallon aquariums. They both were fed a homemade fish food recipe, but the experimental group had fresh garlic extract added to its food. The fish were held for two months, with half receiving the garlic-laced food. After that time, all the fish were euthanized and dissected. Of the experimental group, all of the fish but two showed a complete absence of any worms or eggs. One fish still had one worm, while the other one had eight. Neither fish had any eggs present at that time. The one fish that still had eight worms was noted as being the smallest of the group. It was theorized by the article's author that being low in the pecking order had contributed to this particular fish's not getting enough to eat, and therefore possibly not ingesting a sufficient quantity of the garlic to make a difference. In contrast, the untreated control group had an average of two worms and 14.6 eggs per fish upon dissection. This would seem to show that garlic can be used to treat nematode infestations in freshwater angelfish.

But this study, like the other ones, has some problems. Foremost, a number of the fish from each group, 12 from the experimental group and 11 from the control group, died prematurely. This stopped the author from completing a statistical analysis of the study's results. These fish all apparently suffered from a ruptured lower intestine from the colonic wash procedure; in short, death by enema. Quick poll question; how many of you all are shifting uncomfortably in your seats or clenching tightly as you read this? These deaths reduced the total number of study participants to the point at which "a definitive conclusion on the effectiveness of garlic cannot be made."

Additionally, this study, like several of the others, also used fresh garlic. This again begs the question of whether or not commercial preparations are going to be effective after being processed and then sitting on a shelf for an undetermined amount of time at distributor, wholesaler and retailer locations. And along those same lines, what type of 'fresh garlic' are people using? I imagine just like all other commercially grown crops, garlic too has been selectively bred over the decades to develop varieties that differ in taste, texture, size, smell, etc. I don't believe whether or not the variety of garlic used affects the allicin concentration has been investigated.

And lastly, these were freshwater fish. There is no telling whether or not these results (if later repeated, analyzed and statistically verified) would hold true for all susceptible species of saltwater fish or all the potential intestinal parasitic worms that they carry.

Kelly Jedlicki's Western Marine Aquarium Conference Presentation:

To properly discuss the use of garlic, we really need to go back to the origins of garlic's use for ornamental marines and revisit the presentation Kelly Jedlicki gave at the 1998 Midwest Marine Aquarium Conference in Michigan. It was there that the idea of feeding our fish garlic was first introduced to the saltwater hobby. Now, I must admit, I was not lucky enough to attend this conference firsthand. But, I know Kelly rather well now, and we have discussed this topic on numerous occasions.

Kelly was giving a presentation on general pufferfish care. Part of her discussion centered on the number of fish that she had received that were parasitized with internal worms. In looking for a treatment that was safe and effective, she stumbled across garlic. At this conference, she shared her anecdotal experience of garlic being an effective dewormer. She also happened to mention in passing that she noticed a general decrease in occurrences of Marine Ich/Cryptocaryon irritans when using this garlic treatment. That's it. This does not sound like a ringing endorsement to me. Nor was this a controlled study demonstrating that garlic had an effect on Marine Ich/Cryptocaryon irritans. But none of that seems to matter because from there the legend of garlic spread far and wide. Why are so many people willing to go with this "treatment" based solely upon this one innocuous, anecdotal report? I hate to say it, but I believe laziness had to play at least part of a role. Consider the alternative, proven treatments for an infected tank. In the lack of an easily available magic bullet, the hobbyist has to tear apart the entire aquarium, remove all the fish to a second quarantine system and treat them with hyposalinity or copper while leaving the display empty of fish for a month or two. Or, the aquarist can simply leave the fish in the display and add a couple of drops of this garlic extract to their food and they should heal on their own. When put in those terms, who wouldn't pick the garlic alterative?

Summary:

To recap, garlic's use as an appetite stimulant is questionable at best. It seemed to have a positive effect when injected into fish that were infected with a bacterium. It can kill the freshwater Ich parasite Ichthyophthirius multifiliis when dosed in rather high concentrations in the water. And, it might be an effective dewormer in freshwater fish. But, none of that means it will do anything against Marine Ich/Cryptocaryon irritans when added to the food of infected fish.

So, now that we know what has been studied regarding garlic, it should be readily apparent that there is still much that we don't know about garlic's use as a treatment, particularly against Marine Ich/Cryptocaryon irritans. I hope to shed some light on this in the coming months with a controlled study testing the effectiveness of garlic extract on fish exposed to Marine Ich/Cryptocaryon irritans. Hopefully, I will be able to determine whether garlic has any effect against this parasite, independent of natural acquired immunity. Until such time as that is proven, use a garlic treatment at your (and your fishes') own risk.

References:

Ashdown, Denise & Gary Violetta. 2004. "Using Garlic as an Appetite Stimulant in Sand Tiger Sharks (Carcharias taurus)." Drum & Croaker, January 2004, Volume 35, pages 59-63.

Buchmann, K., P. B. Jensen, & K. D. Kruse. 2003. "Effects of Sodium Percarbonate and Garlic Extract on Ichthyophthirius multifiliis Theronts and Tomocysts: In Vitro Experiments." North American Journal of Aquaculture, Volume 65, Number 1, pages 21-24, 2003.

Colorni, Angelo, Rami Avtalion, Wayne Knibb, Evelyn Berger, Barbara Colorni, & Bracha Timan. 1998. "Histopathology of sea bass (Dicentrarchus labrax) experimentally infected with Mycobacterium marinum and treated with streptomycin and garlic (Allium sativum) extract." Aquaculture 160(1998)1-17.

Colorni, Angelo & Peter Burgess. 1997. "Cryptocaryon irritans Brown 1951, the cause of 'white spot disease' in marine fish: an update." Aquarium Sciences and Conservation, volume 1, pages 217-238.

Fairfield, Terry. 1996. "Garlic & Your Aquarium: A Preliminary report on Allium sativum and fishkeeping." Aquarium Fish Magazine, January 1996, pages 79-83.

Jedlicki, Kelly. pers. comm.

Montgomery-Brock, Dee, Vernon T Sato, James A Brock, & Clyde S. Tamaru. 2001. "The Application of Hydrogen Peroxide as a Treatment for the Ectoparasite Amyloodinium ocellatum (Brown 1931) on the Pacific Threadfin Polydactylus sexifilis" Journal of the World Aquaculture Society, vol. 32, no. 2, pp. 250-254, June 2001.

Online References:

"Garlic versus 'Marine Ich': Diallyl thiosulfinate activity against Cryptocaryon irritans infestation of marine fish" by Horge Cortes-Jorge Jr.

"Hydrogen peroxide treatment for Amyloodinium sp. on mullet (Mugil cephalus) fry" by Montgomery-Brock, Dee, Jane Y. Sylvester, Clyde S. Tamaru, & James A Brock.