Rach, J.J., M. P. Gaikowski, and R.T. Ramsay.  2000.  Pivotal Studies to Evaluate the Efficacy 
of Hydrogen Peroxide to Control Parasite Infestations on Cultured Fish at Selected Fish 
Hatcheries.  Submitted to the U.S. Food and Drug Administration Center for Veterinary 
Medicine.  April 13, 2000.  279 pp.



The efficacy of hydrogen peroxide to control parasite numbers on rainbow trout 
(Oncorhynchus mykiss) was evaluated in three clinical field trials conducted at two 
Wisconsin Department of Natural Resources hatcheries.  In separate trials, rainbow trout 
were transferred from the source culture unit into a test system of 12 individually 
plumbed tanks.  Each tank was supplied with a continuous flow of hatchery water at a 
flow rate providing an exchange rate similar to that of the culture unit. Fish in trials 1 and 
2 were exposed to hydrogen peroxide concentrations of  50, 100, or 200 µL/L for 30 min 
once every-other-day for a total of three treatments.  Fish in trial 3 were exposed to 
hydrogen peroxide concentrations of  50, 100, or 
200 µL/L for 30 min once every-other-day for a total of three treatments.  Pre and post-
treatment (analyzed 4 h after last treatment, except in Trial 3 analyzed at 14d ) skin and 
gill samples were microscopically examined to identify and enumerate external parasites.    
The severity of the infestation was classified as low (1-10 organisms), moderate (11-20), 
or high (?21).  Ambiphrya numbers on the skin of the test fish was high at the inition of 
trial 1.  Post-treatment examinations indicated Ambiphrya was eliminated from all treated 
fish, while control fish remained highly infested with Ambiphrya.  In trial 2 pretreatment 
examinations of skin and gill samples indicated a high infestation of the trematode 
Gyrodactylus (skin) and the protozoan Trichodina (gills) on all fish.  Post-treatment 
examinations of treated fish revealed Gyrodactylus was eliminated from the skin, 
however, high numbers of Trichodina remained on the gills.  All control fish remained 
highly infected with Trichodina (gills) and Gyrodactylus (skin).  High numbers of 
Ambiphrya were present on the skin of test fish in trial 3.  Post-treatment skin 
examinations indicated Ambiphrya was eliminated from most treated fish (56 %), even 
though the last treatment was applied 14 d previously.  Control fish remained highly 
infested with the parasite.  Hydrogen peroxide treatments were efficacious in the control 
of the protozoan Ambiphrya and the monogenetic trematode Gyrodactylus.