Decline in Iodine Concentration of Iodophor during Water Hardening of Salmonid Eggs and Methods to Reduce This Effect

Abstract

Abstract Iodophor iodine concentrations were measured during water hardening of eggs of chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch). Unrinsed and rinsed eggs were water hardened in buckets with varying volumes of uncirculated or circulated iodophor. Iodine concentrations declined immediately when unrinsed eggs were exposed to either uncirculated or circulated iodophor, but not if eggs were rinsed briefly in iodophor before exposure to the water-hardening solution. In all tests, iodine concentrations in and above the egg mass declined during the 1-h water-hardening process. Reusing iodophor to water harden a second volume of eggs resulted in substantially lower iodine concentrations than with first-use iodophor. Iodine concentrations within the egg mass in uncirculated iodophor were inversely correlated with distance from the top of the egg mass–iodophor interface. Increasing the volume of uncirculated iodophor relative to the volume of eggs did not substantially raise iodine concentrations above the eggs. Circulating the iodophor through the egg mass resulted in uniform iodine concentrations at all locations. Iodine concentrations declined more rapidly when equal volumes of iodophor and eggs were used in circulation tests than when four times more iodophor than eggs was used.