Iodine Concentrations Prior to Initial Incubation Do Not Impact the Bacterial Communities of Landlocked Fall Chinook salmon Eggs at the Eyed Stage of Development

Abstract

Using iodine solutions to disinfect newly-spawned salmonid eggs is well established. This study examined the bacterial communities of eggs from five landlocked Chinook salmon Oncorhynchus tshawytscha females subjected to 10-minute treatments’ of 100, 200, or 400 mg/l of active iodine prior to hatchery incubation. Bacterial sampling of the eggs occurred prior to disinfection, immediately after disinfection and 28-days later at the eyed stage of development. Hatchery incubation water was also sampled. The number of cultivable bacteria on the external membrane of freshly-spawned eggs ranged from 10 to over 66 colony-forming units. All of the iodine treatments significantly reduced the number of bacteria compared to pretreatment samples, but there were no significant differences among the treatments. Numbers of cultivable bacteria on eggs at the eyed stage after 28 days of incubation were approximately 105 times greater than those observed on the freshly-spawned eggs. There were no significant differences in egg survival among the iodine treatment groups. Acinetobacter dominated the egg surface prior to iodine disinfection, and Psychrobacter also was common. Flavobacterium was the most prevalent bacterial genus from eyed-eggs, representing over 43% of the sequences. Vibrio and Variovorax were also abundant. The bacterial flora of the hatchery water was dominated by Proteobacteria, especially Pseudomonas species, with Massilia, Zoogloea, Leptospirillum, and Rhodococcus also abundant. No effects of iodine treatment level on the abundance or genera of bacteria on eyed-eggs were evident.