For years, hatcheries in Washington (USA) and elsewhere have experienced unexplained mass mortality events in which entire cohorts of larvae do not survive through setting (transition from mobile larval to sessile juvenile phase). Investigations into known diseases, genetics, and water quality, among other factors, yield no direct correlations to these mortality events. Therefore, it has been proposed that more subtle shifts in the microbiome and/or water quality may be causing larval mortality. A full characterization of the resident microbial community (microbiome) in a hatchery could provide insight into the baseline microbiome and deviations from the baseline that may contribute to mortality events.