Efficacy of 35% PEROX-AID (Hydrogen Peroxide) in Reducing an Infestation of Gyrodactylus salmonis in Freshwater-Reared Rainbow Trout

Abstract

Gyrodactylus salmonis is a monogenean ectoparasite that can infest a variety of captive-reared salmonid fishes. The physical damage inflicted during severe infestations can cause osmoregulatory disturbances and potentially render individuals more vulnerable to secondary pathogens. If not treated, G. salmonis infestations can reduce growth and survival in affected fish populations. Many chemical compounds have been used to treat Gyrodactylus infestations; however, little information has been published about the use of hydrogen peroxide (H₂O₂) for Gyrodactylus control. Consequently, we conducted a trial to evaluate the efficacy of H₂O₂ in reducing a natural infestation of G. salmonis in freshwater-reared, adult rainbow trout Oncorhynchus mykiss. Triplicate tanks of adult rainbow trout (20 fish per tank; length = 45.6 ± 5.8 cm and weight = 1.3 ± 0.4 kg, mean ± SD) were exposed to a static bath of H₂O₂ at a target dosage of 50 mg/L or hatchery water (sham treatment) for 30 min/d on two alternate days. Treatment efficacy was assessed at 2 and 7 d posttreatment via light microscopy examination of skin scrapes (one per fish) taken from 10 fish per tank on each day. At 2 d posttreatment, the mean abundance of G. salmonis in the H₂O₂-treated group (0.1 ± 0.3 G. salmonis individuals per skin scrape) was significantly different from that observed in the sham-treated group (34.4 ± 43.2 individuals per skin scrape). Also, at 7 d posttreatment, the mean abundance of G. salmonis in the H₂O₂-treated group (0.1 ± 0.3 individuals per skin scrape) was significantly different from that observed in the sham-treated group (38.5 ± 77.4 individuals per skin scrape). The percent reduction in mean abundance (treated group compared with control group) was greater than 99% at both 2 and 7 d posttreatment. In conclusion, the H₂O₂ treatment regimen that we used significantly reduced a natural infestation of G. salmonis in freshwater-reared, adult rainbow trout.

Received May 18, 2011; accepted August 21, 2011

ACKNOWLEDGMENTS

We thank Sean Henderson and Ron Hopper at the USFWS Ennis NFH, Ennis, Montana, and Ken Peters at the USFWS Bozeman FHC, Bozeman, Montana, for their help conducting the trial. We thank Eric Leis at the USFWS La Crosse FHC, La Crosse, Wisconsin, for identifying G. salmonis.