Part 2 Life of a Rainbow Trout
We are back with Part 2 in our series of the Life of a Rainbow Trout at Sterling Springs Hatchery. In Part 1 of the Life of a Rainbow Trout, we left off where the eggs had been rolling in the McDonald jars for approximately 11 days and the coloration of the jars has begun to change from ta light pink color to a darker red.
The color change means the sac fry are emerging from the eggs. The newly emerged sac fry, also called Alevins (pronounced AL-uh-vin), hatch with their yolk sacs still attached. Unable to eat, they rely on the yolk to feed them.
Once all of the sac fry have emerged, we empty the jars into the troughs. We pour the McDonald jars containing all the sac fry through a wire mesh screen. The screen separates the sac fry from any dead eggs and debris that were also in the jars.
Dead Eggs, Shells, and Debris
The sac fry easily slip through the special screen, falling to the bottom of the raceway leaving behind all of the blank eggs, leftover egg shells, and debris. We count the blank eggs to determine the number of eggs that were not viable.
The sac fry will now lie on the bottom of the trough for approximately 11 to 14 days. During the 11 to 14 days, the sac fry consume their yolk sac. As the yolk sac disappears, the belly of the fry will “button-up” and they will soon “swim-up”. Once the sac fry consume their yolk sac they are now called fry. As soon as the fry swim to the surface they gulp air to fill their swim bladders. Their next goal is to begin the search for food in the water column.
Rainbow Trout Sac Fry
When about 90% of the fry are swimming in the water column, we begin feeding them small pinches of food. We drop the food in the water with care so that it will likely be consumed by the fry. Otherwise, if the food lands on the bottom of the trough it can later become moldy.
The following days bring with them even more pinches of food until all of the fish are feeding heavily on the water surface. Once the fish are feeding well and the feed is disappearing, the rearing units must be cleaned daily with special care to remove all deformed, dead, or dying fish, along with any fecal material. The moralities must be counted on a daily basis.
Now the fry eat and grow. Stay tuned for Part 3 of Life of a Rainbow Trout.
If you missed it, you can catch up on the the first stages of a Rainbow Trout’s life at Sterling Springs Hatchery at Part 1 of Life of a Rainbow Trout.
