Anthelmintic effects of 75 ppm hydrogen peroxide treatment on the monogeneans Benedenia seriolae, Neobenedenia girellae, and Zeuxapta japonica infecting the skin and gills of greater amberjack Seriola dumerili

Abstract

Infection by the capsalid monogeneans Benedenia seriolae and Neobenedenia girellae, and/or the microcotylid monogenean Zeuxapta japonica can be a problem when the greater amberjack Seriola dumerili (Carangidae) is commercially cultured. Effective control measures against these monogeneans that are safe for S. dumerili, especially during the summer when the ocean temperature increases, are still needed. Therefore, we investigated: 1) the anthelmintic effects of 75 and 300ppm hydrogen peroxide on these monogeneans in vitro trials, 2) the safety of hydrogen peroxide for S. dumerili at various concentrations for 6h, 3) the anthelmintic effects of 75 and 300ppm hydrogen peroxide on N. girellae infecting S. dumerili in vivo at water temperatures of 25 and 30°C, and 4) the efficacy of 75ppm hydrogen peroxide against the monogeneans infecting S. dumerili in a summer field trial. We found that for the in vitro trials, B. seriolae and N. girellae that were exposed to 75ppm hydrogen peroxide for 30 or 60min were more strongly affected than were those exposed to 300ppm hydrogen peroxide for 3min. In addition, the bodies of all Z. japonica contracted, the extent of contraction in those exposed to 75ppm hydrogen peroxide for 30min was greater than those exposed to 300ppm hydrogen peroxide for 3min. Uninfected fish suffered severe effects when exposed to 150 or 300ppm hydrogen peroxide, but when exposed to 75ppm hydrogen peroxide for 6h, their survival, appetite, and swimming behavior were unaffected. We found that N. girellae infection levels in fish exposed to 75ppm hydrogen peroxide for 30min in vivo were significantly lower than those exposed to 300ppm hydrogen peroxide for 3min at 25 and 30°C (P<0.01). In addition, complete elimination of B. seriolae, N. girellae, and Z. japonica was achieved under the condition of 75ppm hydrogen peroxide, 30min, and a water temperature of 28.5°C in the field trial. This treatment did not influence the behavior of the fish in the in vivo trials. Thus, treatment of cultured S. dumerili in a bath of 75ppm hydrogen peroxide for 30min should control these monogeneans. Statement of relevanceS. dumerili is a major commercially cultured fishes in Japan. These fish are cultured in floating net pens or cages, but the capsalid monogeneans B. seriolae and N. girellae can infect their skin and are, therefore, destructive parasites. Additionally, the microcotylid monogenean Z. japonica, which infects the gills of S.dumerili, is also a destructive parasite. To eliminate these parasites, fish may be fed praziquantel-supplemented feed, submerged in a freshwater bath for 2- to 5-min, or placed in a hydrogen peroxide bath. However, none of these measures simultaneously dislodge B. seriolae, N. girellae, and Z. japonica. Orally administered praziquantel is markedly poor against N. girellae infecting S. dumerili and Seriola quinqueradiata, and the freshwater treatment is not very effective when the fish are infected with Z. japonica. Additionally, the hydrogen peroxide treatment negatively affects fish health and viability, especially in the summer when water temperatures are higher and the parasite doubling and maturation rates increase. Thus, any parasite control measure must be performed frequently during the summer.For the study reported in our enclosed manuscript, we investigated: 1) the anthelmintic effect of hydrogen peroxide treatment at concentrations of 75 and 300ppm on those monogeneans in vitro, 2) the effects of hydrogen peroxide at various concentrations for 6h on S. dumerili, and 3) the anthelmintic effect of hydrogen peroxide treatment at concentrations of 75 and 300ppm against N. girellae in vivo and the effect of 75ppm hydrogen peroxide against these monogeneans in a field trial.This study shows that 75 ppm hydrogen peroxide for 30min could be for a way to eliminate B. seriolae, N. girellae, and Z. japonica when they infect commercially cultured S. dumerili. In addition, the treatment with 75ppm hydrogen peroxide for 6h did not negatively impact fish survival, swimming ability, and appetite. Thus, treatment of cultured S. dumerili in a bath of 75ppm hydrogen peroxide for 30min should control these monogeneans.