Oxygen Availability Provides a Signal for Hatching in the Rainbow Trout (Salmo gairdneri) Embryo

The hatching of rainbow trout (Salmo gairdneri) embryos can be stimulated by subjecting them to low oxygen partial pressures [Formula: see text] during the final days of incubation or delayed by elevating [Formula: see text]. Most embryos develop the ability to hatch between days 26 and 27 of incubation at 12 °C. During this time, similar hatching frequencies are obtained at any [Formula: see text] below a critical value in the 94–135 mm Hg (6.5–9.3 mg/L) range (1 mm Hg = 133.322 Pa). The [Formula: see text] required for continued incubation increases with developmental time such that hatching cannot be delayed beyond day 30 at 12 °C. These results indicate that oxygen availability influences the time at which trout embryos hatch and that hatching occurs when hatchable embryos are confronted with an ambient [Formula: see text] that is inadequate to satisfy aerobic metabolic requirements.