Part 1 Life of a Rainbow Trout
Have you ever wondered where all of the Rainbow Trout in Arizona come from? Well you are in luck! This four part series will walk you through the life of a Rainbow Trout from the beginning to end.
On December 6, 2016 Sterling Springs Hatchery received a second shipment of 218,000 Rainbow Trout eggs that are combined with 75,000 Rainbow Trout eggs. These eggs will soon become some of the state’s stockable trout for next season.
The eggs arrive from Ennis National Fish Hatchery in Ennis, MT via Federal Express. They ship the day before and arrive at the hatchery within 24 hours. The eggs come in cardboard boxes lined with Styrofoam and filled with ice. The ice keeps the eggs cool and moist. After the eggs arrive, we carry the boxes directly from the truck to the hatchery intake room.
The Rainbow Trout eggs are called “eyed eggs” and have been fertilized before they are shipped. They have begun the development process. The eggs are at a point where the coloration of the eyes is evident through the shell of the egg. The eggs are very easy to handle and are durable at this stage.
Firstly, we water harden and temper the newly delivered eggs from their incoming temperature to the temperature of the hatchery water. To temper the eggs, we add ice to the eggs to lower the temperature and add fresh hatchery water to the sink to raise the temperature. This process re-hydrates the eggs and closes up the micropiles in the eggs shells. We follow this procedure in order to keep the disinfecting process from killing the eggs. The micropile is the small opening in the eggs that allow the sperm from the male fish to enter the egg shell during spawning.
The next step the eggs go through is sampling the eggs to determine their size for the (enumerating) counting process. There are two ways to determine the total number of eggs. The first method is called the Von Bayer Trough. We place the eggs in a single row in a trough of a designated size. You can count the eggs in this trough and as a result find the number of eggs per ounce. This method is repeated at least three times to give the most accurate estimate.
The second type of sampling process is called displacement. We pat 50 eggs with a paper towel to rid them of any excess water. Next, we place the eggs in a measuring cylinder. The amount of milliliters (ml) displaced in the cylinder gives us the estimate of eggs per ml. We repeat the process at least three times to get the best average of size in order to estimate the total number of eggs.
Disinfecting and Hatching
After the sampling process is complete, we place the eggs in an iodine bath for at least 10 minutes. This thoroughly kills any bacteria that may be hitchhiking from the other hatchery. Then, we measure the eggs and place them in equal numbers in upwelling incubator jars also called “McDonald Jars”. The upwelling jars are probably the simplest and least problematic hatching system. The system uses fresh, cold water that just rolls through the jars bringing with it fresh, oxygenated water for the eggs. Oxygen is very important because without oxygenated water, the eggs will die or suffer from deformities. The rolling motion, due to the inflow of water down a small tube in the center of the jar, keeps fungus from growing in the jar and causing the eggs to suffocate.
Once all the eggs are in the jars, the water system will roll the eggs for approximately 11 days or until all the eggs have hatched out of their shells and are swimming around as sac fry. As the sac fry hatch out of their shells, we clear the egg shells out of the overflow trough behind the jars. We clear out the overflow numerous times a day.
As the sac fry finish hatching, the overflow trough has fewer and fewer egg shells. Afterward, we move the sac fry into a trough. We move the sac fry because the jars change from light pink color to a dark red. This is due to the yoke sacs on the fry becoming very evident as the fry emerge from the eggs. Some of the eggs will be white or pale because they are blanks or dead eggs. We count and discard the blanks during the transfer of the fry into holding tanks.
As with most processes in aquaculture, keeping it simple is often best! As well as is keeping all of the units clean. Stay tuned for Part 2 of the Life of a Rainbow Trout to learn about the next stages our stocked Rainbow Trout go through at Sterling Spring Hatchery.