Actually there are numerous scientific studies that has come out over the past decade, but most if not all of these studies with garlic involve freshwater species. I would imagine that it's a matter of funding, and/or importance in the marine area, but some groups in the freshwater sector are taking a very strong look at garlics potential, and the results are no longer just anecdotal.
Also, while allicin is the main active ingredient found in garlic, it is only
one sulphur compound amongst many compounds & enzymes found in Allium sativum, and it would be more than just a bit presumptuous at this stage of the research taking place in this area to believe that allicin is the
only active compound that has any health benefits associated with its use in aquaculture. There is much more involved with regards to the bioactive components in garlic, than just allicin.
Some of the studies that I've read actually involved garlic
powder, and yet yielded some very positive results. In most of the aquaculture studies that I am aware of the garlic that was used was not fresh, or a derivative was used.
The only studies I'm aware of that involved liver damage speculation, or any type of short or long term health risk to a marine or freshwater fish, involved the pure form of allicin fed at elevated levels. I discussed one such study in detail with one of the research scientists involved with a study that took place a couple of years ago in the UK. Unfortunately he couldn't see beyond his PhD.
On the other side of the coin I have seen
scores of marine species consume pellet feed that contained garlic at a low inclusion rate,
on a daily basis for close to 15 yrs, with no negative health issues whatsoever.
While the research & studies posted below don't involve the marine species that members here might keep in their tanks, I don't think that it's a huge leap of faith to extrapolate at least some of this information to marine species.
A. M. Shalaby et al. EFFECTS OF GARLIC (Allium sativum) AND CHLORAMPHENICOL ON GROWTH PERFORMANCE, PHYSIOLOGICAL PARAMETERS AND SURVIVAL OF NILE TILAPIA (Oreochromis niloticus).
Fish Hatchery and Reproductive Physiology Department, Central Laboratory for Aquaculture Research, Abbassa, Abo-Hammad, Sharkia, Egypt
J. Venom. Anim. Toxins incl. Trop. Dis., 2006, 12, 2, p.196
http://www.scielo.br/scielo.php?scri...lng=en&nrm=iso
While the document linked to above is a very long read, in the end the authors state:
Quote:
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Finally, from the obtained results it could be recommended that garlic (Allium Sativum) may be used as a growth promoter and antibiotic for the treatment or prevention of diseases and for enhancing fish tolerance to environmental stress (62); therefore garlic powder should be added to the diet of freshwater fish.
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In this particular study the inclusion of garlic at a rate of 3% (via garlic powder) has shown to increase the overall digestibility of protein, carbohydrates, and fat (ie; better growth), as well as to lower the total bacteria count within the intestine, muscles, and water column.
In Norway, the Austevoll Aquaculture Research Station has studied the use of garlic as a natural biocide against sea lice, with positive results.
http://www.onefish.org/servlet/CDSSe...50cyYzNz1pbmZv
There are other studies that have also shown very positive results in using garlic as a more natural way to control various pathogens.
Effect of Allium sativum on the immunity and survival of Labeo rohita infected with Aeromonas hydrophila
S. Sahu, B. K. Das, B. K. Mishra, J. Pradhan and N. Sarangi
Aquatic Animal Health Division, Central Institute of Freshwater Aquaculture, Kausalyaganga, Bhubaneswar, India
Journal of Applied Ichthyology, Volume 23 Issue 1, Pages 80 - 86
Quote:
Summary
The aim of this study was to evaluate dietary dosages of garlic on the immune response and disease resistance against infections due to the opportunistic pathogen Aeromonas hydrophila in Labeo rohita fingerlings. Garlic, Allium sativum, was incorporated into the diets (0%, 0.1%, 0.5% and 1.0%) of rohu, L. rohita fingerlings (10 ± 2 g). Every 20 days, different biochemical (serum total protein, albumin, globulin, albumin : globulin ratio, blood glucose), haematological (WBC, RBC and haemoglobin content) and immunological (superoxide anion production, lysozyme activity and serum bactericidal activity) parameters were evaluated. Superoxide anion production, lysozyme, serum bactericidal, serum protein and albumin were enhanced in garlic treated groups compared with the control group. After 60 days, fish were challenged with A. hydrophila and mortality (%) was recorded up to day 10 post-challenge. Survival decreased in control group (57%) up to day 10 after infection. However, this was increased in the garlic treatment group, i.e. 85% survivability in the 1 g garlic kg−1 (B group) and 5 g garlic kg−1 (C group), and 71% survivability in the 10 g garlic kg−1 (D group), respectively. These results indicate that Allium sativum stimulates the immunity and makes L. rohita more resistant to infection by A. hydrophila.
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And another ..............
EFFECT OF GARLIC ON THE SURVIVAL, GROWTH, RESISTANCE AND QUALITY OF OREOCHROMIS NILOTICUS
Salah Mesalhy Aly, Nashwa Mahmoud Abdel Atti* and Mohamed Fathi Mohamed
The WorldFish Center, Research Center for Africa & West Asia, Abbassa, Sharkia, Egypt. Dept of Food Hygiene, Animal Health Research Institute, Ismailia Laboratory, Egypt.
http://ag.arizona.edu/azaqua/ista/IS...%20Meselhy.pdf
In Israel, researchers from the Ben Gurion University aquaculture dept. are also experimenting with allicen, the active ingredient in garlic, for its anti-bacterial properties.
http://www.foodengineeringmag.com/Ar...100000f932a8c0
No doubt there are many more studies that have or currently are taking place within the aquatic industry, the examples above are just a few that I am aware of.
HTH