Salmonid populations of the Central Valley of California have been in decline for decades, making hatchery practices that combine conservation strategies with targeted research essential to optimize recruitment to adulthood. Hatchery populations generally exhibit a higher incidence of precocious male maturation than natural populations. However, optimal hatchery management practices pertaining to incubation, feeding, and genetic predisposition have yet to be optimized to lower the incidence of precocity in hatchery-reared male spring-run Chinook Salmon Oncorhynchus tshawytscha. To further assess this, we conducted a 2 × 2 factorial experiment exploring the effect of embryo incubation temperature (cold or warm) and post-ponding ration (high or low) on incidence of age-1 precocious male maturation. Fertilized eggs from each parental cross were placed among each treatment group to control for genetic variation and track any genetic predisposition. Precocity rate at year 1 was affected by incubation temperature and feed rate. There were also significant differences in growth rate and body condition among the treatment groups during early development. Additionally, the precocious males were nonrandomly produced by the crosses, suggesting a significant parentage effect on precocity. Optimization of Chinook Salmon rearing techniques is critical-not only to lessen the incidence of precocity and identify the causal parameters, but also to maximize successful reintroduction.