Broodstock are adult fish that produce eggs and sperm. Seven different strains of rainbow trout broodstock are cultivated at Ennis National Fish Hatchery. The strains are named for the locations from which they came.
- McConaughy (Nebraska)
- Eagle Lake (California)
- Shasta (California)
- Erwin/Arlee Cross (Tennessee)
- Fish Lake (Utah)
- Arlee (Montana)
- Harrison Lake (Montana)
Some of the eggs from each strain are hatched and reared at Ennis for future broodstock. They mature at 2 or 3 years of age and are kept for spawning another 2 or 3 years.Geneticists are hired periodically to monitor the genetic variability of the broodstock using a process called electrophoresis (identifying amino acids within the fish). When monitoring shows that genetic variability is deteriorating, eggs or sperm will be shipped to the Ennis National Fish Hatchery (NFH) from outside sources to restore genetic variability of the stock.
Broodstock at Ennis NFH may grow 32 inches and weigh 25 pounds. Once the fish are no longer needed as broodstock, they are transported and released in kids ponds in Montana where young anglers test their skill at landing big fish.
Spawning, Fertilizing, and Incubating Eggs
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. Milt (a milky substance containing the sperm) from the male fish is mixed thoroughly with the eggs. Microscopic sperm cells in the milt have a long whip-like tail which propels them rapidly around the eggs. When a sperm cell enters the micropyle (a microscopic hole in the egg) it unites with the nucleus of the egg and fertilization is complete. Fertilization must take place very quickly because the sperm cell only lives about 30 seconds in water!
After fertilization, eggs are put in incubators where they continue to develop until Ennis NFH personnel can see the eyes of the tiny fish inside the egg. The eggs are then ready to be processed and shipped.
Transporting Fish Eggs
How would you like to be responsible for packing and shipping 20 million fish eggs every year? You would have to be very careful because the eggs are fragile!
First, it is necessary to separate live eggs from dead eggs. To do this, the eggs are poured into a sorting machine that uses optical sensing to separate the orange-colored live eggs from the white dead eggs. Usually about 5% - 8% of the eggs are white.
The live eggs are then packed into specially constructed trays. The trays are stacked in an insulated box topped with a tray containing crushed ice. The ice melts during shipping, keeping the eggs both cool and moist. Packed this way they can stay alive at least two days. Eggs are sent by express carrier and usually arrive at their destination within 36 hours.
Last updated: January 23, 2012