They mature at 2 or 3 years of age and are kept for spawning another 2 or 3 years. When monitoring shows that genetic variability is deteriorating, eggs or sperm will be shipped to the Hatchery from outside sources to restore genetic variability of the stock. Broodstock at Ennis National Fish Hatchery may grow 32 inches and weigh 25 pounds. Once the fish are no longer needed as brood stock, they are transported and released in public waters in Idaho and Montana where anglers may test their skill at landing big fish. When a female is ready to release her eggs, a hypodermic needle connected to an oxygen bottle is inserted into the body cavity.
Air pressure forces the eggs out of the body cavity into a pan.
This process does not hurt the fish. Microscopic sperm cells in the milt have a long whip-like tail which propels them rapidly around the eggs. After fertilization, eggs are put in incubators where they continue to develop until Hatchery personnel can see the eyes of the tiny fish inside the egg. The eggs are then ready to be processed and shipped. First, it is necessary to separate live eggs from dead eggs.