The commercial pellets I feed have garlic in them, at an inclusion rate that
has proven to be effective for fish. (3%) No need to feed garlic oil, or fresh, garlic powder can be just as effective.
http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1678-91992006000200003&lng=en&nrm=iso
While the document linked to above is a very long read, in the end the
authors state:
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.
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
In this particular study the inclusion of garlic at a rate of 3% (via garlic
powder) has shown to increase the overall digestibilty 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/CDSServlet?status=ND0zODEzMi50b3JsaWJJUEUzMjg5NiY2PWVuJjMzPWRvY3VtZW50cyYzNz1pbmZv
In most of the aquaculture studies that I am aware of the garlic that was
used was not fresh, or a derivitive was used.
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
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.
And yet another study .........
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/ISTA8/FinalPapers/Growth%20pdf/22%20salah%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/Articles/Column/f0208f4ab52f8010VgnVCM100000f932a8c0____
HTH