Oxygen requirements of whitefish and vendace (Coregoninae) embryos at final stages of their development

Whole eggs and excised embryos of vendace ( Coregonus albula) and whitefish ( C. lavaretus) were exposed to various partial pressures of oxygen for 60 min at 4 and 8 °C, and their heart rate was measured. Embryos responded to hypoxic conditions by a decrease in heart rate (bradycardia). The intensity of bradycardia increased at decreasing partial pressures of oxygen and it was always higher in the whole-egg embryos than in the excised ones. The lower acceptable limits of partial pressures of oxygen for embryos at the developmental stage of eye movement visible and at 4 °C were estimated as about 30.6 mm Hg (2.5 mg/l dissolved oxygen concentration—DO) for whitefish and about 38.8 mm Hg (3.2 mg/l DO) for vendace. At 8 °C, respective values were about 54.0 mm Hg (4.0 mg/l DO) and 52.7 mm Hg (3.9 mg/l DO).