Oxygen concentration in the water boundary layer next to rainbow trout (Oncorhynchus mykiss) embryos is influenced by hypoxia exposure time, metabolic rate, and water flow

Abstract

The objective of this study was to examine the influence of hypoxia exposure time, metabolic rate, and water flow rate on the O2concentration in the boundary layer outside and inside the chorion of rainbow trout ( Oncorhynchus mykiss ) embryos. Oxygen consumption, growth, and dissolved O2in the boundary layer were measured at 15, 22, and 29 days post fertilization (dpf) from embryos reared in normoxia (O2concentration 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 O2in the boundary layer to the same extent at 15 and 22 dpf; however, at 29 dpf, O2levels were significantly lower in acute relative to chronic hypoxia. At 29 dpf, O2uptake per individual was significantly lower in embryos exposed to chronic relative to acute hypoxia. In addition, mass-specific O2uptake 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 O2is 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.