Susceptibility of Nanophyetus salmincola Cercariae to Formalin, Hydrogen Peroxide, and Seawater.

Abstract

The ability of formalin, PEROX-AID (hydrogen peroxide), and seawater to kill waterborne Nanophyetus salmincola cercariae was evaluated invitro. Newly emerged cercariae survived for extended periods in freshwater, with 53-73% survival occurring in negative control groups after 24h. Exposure to dilutions of formalin reduced this survival time, with 0% of cercariae surviving after30min in 450μL/L, 40min in 225μL/L, and 300min in 113μL/L. Exposure to PEROX-AID (hydrogen peroxide) for 1h resulted in reduced cercarial survival (16.4%) only at the highest concentration (100μL/L), compared with 100% survival in the untreated controls and all lesser concentrations. Exposure to dilutions of seawater resulted in reduced cercarial survival only at high salinities (15.2-30.3‰), where 10-min exposures resulted in 0-20% survival. These results provide insights into options for prophylactic water treatment at salmonid enhancement facilities that experience high mortalities due to infections with Nanophyetus salmincola. Further, the intolerance of live cercariae to high salinities indicates that exposure to fish occurs primarily in the freshwater portions of watersheds.