Effect of Iodophor Concentration and Duration of Exposure during Water Hardening on Survival of Atlantic Salmon Eggs

Abstract

Because of disease transmission concerns, field studies to evaluate the impact of water-hardening eggs at different concentrations of polyvinylpyrrolidone iodine (iodophor) for various times of exposure have rarely used untreated controls. Additionally, U.S. Fish and Wildlife Service protocol requires a subsequent post–water-hardening surface disinfection for salmonid eggs transferred between stations. The cumulative impact of this second disinfection on survival has not been fully investigated for Atlantic salmon Salmo salar. This study compared the percent of eye-up Atlantic salmon eggs that had been water-hardened with iodophor treatments at 50, 100, and 150 mg active ingredient/L for 30, 60, and 90 min with that of untreated controls and also examined the impact on egg survival of a second iodophor disinfection 5 h after the initial exposure. No discernable mortality resulted from the second (10-min) disinfection. Nontreated eggs had significantly greater survival than any of the iodophor-treated eggs. Contact time with the iodophor solution had the greatest impact on egg survival. When averaged over all concentrations, the decline in egg survival was significant (P < 0.05) when contact time increased from 30 to 60 min. Interaction between iodophor concentration and exposure time was most evident at the high (150 mg/L) concentration, with egg mortality increasing with contact time. Our study suggests that to optimize egg survival, contact with iodophor during water hardening should be no more than 30 min. If a greater disinfection efficacy is desired, an increase in iodophor concentration may be preferable to an increase in contact time.