The objective of this study was to examine the influence of hypoxia exposure time, metabolic rate, and water flow rate on the O2 concentration in the boundary layer outside and inside the chorion of rainbow trout ( Oncorhynchus mykiss ) embryos. Oxygen consumption, growth, and dissolved O2 in the boundary layer were measured at 15, 22, and 29 days post fertilization (dpf) from embryos reared in normoxia (O2 concentration at 100% saturation) and chronic hypoxia (>24 h, 50% saturation) and exposed to acute hypoxia (30 min, 50% saturation). Chronic and acute hypoxia exposure decreased the dissolved O2 in the boundary layer to the same extent at 15 and 22 dpf; however, at 29 dpf, O2 levels were significantly lower in acute relative to chronic hypoxia. At 29 dpf, O2 uptake per individual was significantly lower in embryos exposed to chronic relative to acute hypoxia. In addition, mass-specific O2 uptake in chronic hypoxia-exposed embryos was ~40% less than that of controls but the same as that of acutely exposed embryos. This correlates with reduced growth in embryos exposed to chronic hypoxia. We conclude that boundary layer O2 is lower after 30 min of hypoxia compared with 2 weeks of hypoxia simply because embryos exposed to chronic hypoxia grow slower and consume less O2.