Susceptibility of Nanophyetus salmincola cercariae to formalin, hydrogen peroxide, and seawater.

The ability of formalin, PEROX-AID® (hydrogen peroxide), and seawater to kill waterborne Nanophyetus salmincola cercariae was evaluated in vitro. Newly emerged cercariae survived for extended periods in freshwater, with 53-73% survival occurring in negative control groups after 24 hr. Exposure to dilutions of formalin reduced this survival time, with 0% of cercariae surviving after 30 min. in 450 μL / L, 40 min. in 225 μL / L, and 300 min. in 113 μL / L. Exposure to PEROX-AID® (hydrogen peroxide) for one hour resulted in reduced cercarial survival (16.4%) only at the highest concentration (100 ppm), compared to 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 exposures to fishes occur primarily in the freshwater portions of watersheds. This article is protected by copyright. All rights reserved.