Flavobacterium psychrophilum (Family Flavobacteriaceae), etiological agent of bacterial coldwater disease (BCWD) and rainbow trout fry syndrome (RTFS), causes heavy losses in trout and salmon (Family Salmonidae) aquaculture facilities and hatcheries worldwide, thus negatively affecting food security and fishery conservation efforts. A particularly challenging aspect of BCWD and RTFS is vertical transmission, whereby the bacterium spreads from infected adults to resulting progeny via the eggs and reproductive fluids. In this context, and of particular concern, F. psychrophilum is transmitted intra ova, rendering current disinfection methods ineffective as iodophor is not believed to permeate into the perivitelline space. Traditionally, and in line with current best management practices, eggs are disinfected with iodophor during and or after the water hardening stage (i.e., post-fertilization). Towards breaking the vertical transmission route of this bacterium, a modified disinfection process was evaluated. Herein, eggs were iodophor-disinfected prior to fertilization and closure of the egg micropyle, which contrasts with conventional disinfection, whereby eggs are disinfected after fertilization. In a pilot experiment, unfertilized rainbow trout eggs were artificially infected with a virulent rainbow trout-associated F. psychrophilum isolate (US087) and subsequently iodophor-disinfected (50-100 parts per million [ppm] iodophor; duration of 15-45 minutes) either before and after fertilization or only after. F. psychrophilum was detected solely in fry hatching from eggs that received post-fertilization disinfection only. A similar full-scale experiment was conducted, which tested the efficacy of six different egg disinfection treatments (15-minute pre-fertilization treatment of 50ppm iodophor, 0.75% saline, or no treatment followed by 45-minute hardening in either 100ppm iodophor or water) to reduce or eliminate F. psychrophilum in experimentally exposed rainbow trout eggs. Following F. psychrophilum immersion exposure and egg disinfection treatment, mortalities were recorded, removed daily, and a subset of dead and live eggs and fry of each developmental stage were screened for F. psychrophilum via culture through approximately two months post-hatch. The solely pre-fertilization egg disinfection treatment (50ppm iodophor, 15 minutes) appears promising for reducing egg-associated F. psychrophilum transmission as the bacterium was not detected in any eggs or fry. This contrasts with all other F. psychrophilum exposed experimental treatments, including the traditional disinfection method, from which the bacterium was recovered. Of note, cumulative percent mortality appeared similar between the traditional disinfection method and the solely pre-fertilization disinfection method indicating no apparent detrimental effects on egg viability. This modified egg disinfection method has the potential to reduce the risk of F. psychrophilum vertical transmission in rainbow trout, thereby improving the health and productivity of trout farms and hatcheries.