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