for soundness before being put into the incubators. Incubators control temperature and humidity, and turn the eggs until just before they hatch. Three days before the eggs are scheduled to hatch, they are moved into a hatcher unit, where they are no longer turned so the embryos have time to get properly oriented for their exit from the shell, and the temperature and humidity are optimum for hatching. The eggs will hatch during a period that is often referred to as the hatching window, which can stretch from 24 to 48 hours depending on biological variation. Once the eggs hatch and the chicks are a few days old, they are often vaccinated. Chicks hatched conventionally are provided feed and water first when they reach the rearing farm. In the meantime, they rely on their yolk sac for nutrients. See also Endangered species Minimum viable population Inbreeding depression Oystering machinery References External links Hatcheries and the Protection of Wild Salmon University of Washington Libraries Digital Collections -- Digital Collections -- Fish Hatcheries An ongoing digital collection of images related to fish hatcheries. - Links to hatchery reform projects Poultry farming Intensive farming