The application of hydrogen peroxide as a treatment for the ectoparasite Amyloodinium ocellatum (Brown 1931) on the Pacific threadfin Polydactylus sexfilis

Ectoparasite infections can cause death or a decline in the general health of farm-raised finfish. This paper reports the findings from two studies co nducted to evaluate the efficacy of hydrogen peroxide as a therapeutant for the control of infections of Amyloodinium sp. on cultured Pacific threadfi n Polydactylus sexfilis (locally called "moi"). Threadfin with amyloodinias is collected from a commercial farm were used in both trials. Prior to the trials, and following hydrogen peroxide treatment, the extent of infection was determined by a gill biopsy procedure. An initial trial was conducted i n the laboratory to assess the response of juvenile threadfin and Amyloodin ium sp. trophonts to hydrogen peroxide exposure at four dosages: 0, 75, 150 , or 300 mg/L for 30 min. In a trial on a commercial farm, a hydrogen perox ide treatment at 75 mg/L for 30 min was applied to juvenile threadfin in a grow-out tank. In both trials, hydrogen peroxide was immediately hushed fro m the culture system with seawater after the 30 min exposure period. In the laboratory trial, treatment with 300 mg/L hydrogen peroxide resulted in 10 0% mortality of the exposed group of fish. However, single treatments with hydrogen peroxide at concentrations of 75 or 150 mg/L eliminated Amyloodini um sp. trophonts without causing loss of fish. In the field trial, a single treatment with 75 mg/L hydrogen peroxide greatly reduced levels of Amylood inium infestation, and a second treatment 6 d later reduced Amyloodinium tr ophonts to a nondetectable level. These findings suggest that hydrogen pero xide is a suitable chemical for the treatment of amyloodiniasis of cultured , juvenile Pacific threadfin.