Salmon Embryos (image) NOAA Fisheries West Coast Region Share Print E-Mail Caption Winter-run Chinook salmon embryos (like the ones shown above) hatch from their egg capsules after more than a month-long development period buried in gravel nests. After hatching they spend another month or longer as alevins, buried under gravel continuing to grow by feeding off the energy stored in their yolk sacs until finally they emerge from the gravel as fry. Salmon are especially vulnerable to elevated temperatures during their embryonic stages. Credit Douglas Killam, Calif. Department of Fish and Wildlife. Usage Restrictions Credit Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.