Investigation of the toxicological and histopathological effects of hydrogen peroxide bath treatments at different concentrations on Seriola species and the effectiveness of these treatments on Neobenedenia girellae (Monogenea) infestations

To eliminate B. seriolae and N. girellae, Z. japonica, 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 ineffective against N. girellae infestations in Seriola species, and the freshwater treatment is not effective when the fish are infected with Z. japonica. Additionally, H2O2 treatment at a concentration of 300 ppm (conventional concentration in Japan) negatively affects fish health and viability, especially in the summer when water temperatures are higher and the parasite doubling and maturation rates are increase. Thus, any parasite control measure must be performed frequently during the summer. A bath treatment with 75 ppm H2O2 for 30 min effectively eliminates these parasites and the fish survival, appetite and swimming behavior were unaffected when exposed to 75 ppm H2O2 for 6 h at 25 °C. Therefore, treatment with 75 ppm H2O2 for 30 min is not expected to adversely affect S. dumerili. However, histological analyses of lower H2O2 concentrations have not been performed to determine the effects on the host fish, and experimental proof of the safety of different concentrations is important for the use of this treatment in aquaculture.