Growth, aerobic metabolism, and dissolved oxygen requirements of embryos and alevins of steelhead, Salmo gairdneri

Indirect calorimetry was used to estimate metabolic rates and critical dissolved oxygen concentrations for steelhead (Salmo gairdneri) at intervals between fertilization and complete yolk exhaustion at 6, 9, 12, and 15 °C. As well, tissue growth and yolk utilization were monitored. Energy budgets were constructed and the total amount of energy expended on respiration at each temperature estimated. On average, respiration accounted for 43.2% of the energy mobilized up to 90% yolk utilization. Absolute values agreed well with those estimated by integrating measured metabolic rates over the same period, confirming that measured metabolic rates and critical levels were representative of routine metabolism. Equations predicting metabolic rate and tissue mass as functions of time and temperature are given. Metabolic rate increased in virtually direct proportion to increases in tissue mass as indicated by a mean metabolic mass exponent of 1.05. Metabolic intensities averaged 200, 311, 405, and 548 μg O2∙ g wet tissue−1∙ h−1 at 6, 9, 12, and 15 °C, respectively. Critical oxygen concentrations increased continuously during embryonic development. Levels rose from <1 mg∙ L−1 shortly after fertilization to 7.5–9.7 mg∙ L−1, depending on temperature, just before hatch. Levels abruptly dropped by 2–3 mg∙L−1 at hatch and then declined gradually to reach stable levels of 2.3–4.8 mg∙L−1, depending on temperature, midway through the alevin period. Critical levels at all stages increased with increasing temperature as a direct reflection of increased metabolic demand. It is proposed that maximum critical levels (i.e., those just before hatch) be used to define dissolved oxygen criteria for steelhead in natural waters.