It is no trivial task to produce fish of stocking size, and, in the case of Chinook Salmon, the work involved is considerable. The collection of eggs and sperm is made difficult by the sheer size of the fish involved. That, coupled with working in fast water collecting a hundred or more fish in a session makes for a long hard day. Luckily the river is a long drive from the hatchery, so the trip back gives a brief respite.

Upon arrival, the eggs begin their journey through the hatchery. Ringwood is a Class 3 Facility, meaning that nothing enters the building that may introduce pathogens. Every egg and fish (humans too) must be disinfected lest desease is brought into the building. After the volunteers disinfect their hands and feet, the eggs are brought into the egg-receiving room where they are fertilized. Once milt has been added to the fresh eggs, the eggs are allowed to rest to ensure fertilization occurs. Then, excess milt is washed away by rinsing in water and the eggs are then placed into containers which are immersed in an Isodine solution for disinfection. The eggs remain in the solution for fifteen minutes after which they are rinsed in flowing cold water for an hour. The eggs are then ready to be placed in Heath Tray incubators, which will be their home until they are free-swimming. The eggs are picked for removal of any that have not been fertilized and then 3.5L of eggs is measured and poured into individual trays. Other than chemical treatments to prevent the growth of fungus, the eggs are left undisturbed for the coming weeks.

The length of time the eggs remain in the incubators is determined by their development and growth, both of which are a function of water temperature. The progress of development is measured in Accumulated Thermal Units (ATU). One ATU is equivalent to one degree Celsius for one day. Any given species of fish requires a specific number of ATUs to reach a specific point in its development. Chinook Salmon, for example, require 280 ATU to reach the eye-up stage. How that point is reached is dependent on time and water temperature. For example, if the water temperature is 10 C°, the eggs will eye up in 28 days (10° x 28 days = 280 ATU). Warmer or cooler water will decrease or increase the number of days required to attain the required ATU. Chinook Salmon will hatch at 500 ATU and become free swimming at about 900 ATU. Knowing this, hatchery workers can reliably predict what stage the eggs and alevin will be on any specific date.

Using ATU calculations, it can be determined when the first batch of eggs, will be in the eyed stage and ready for sorting and picking. Prior to eye-up, the eggs are fragile and susceptible to damage by physical movement and shock. Thus the eggs are not disturbed until about the 240 ATU stage. Once the eggs are eyed, they are less likely to be harmed by physical handling. During the preceeding weeks, infertile eggs have turned white, and these will be removed before the eggs are measured again and then returned to the incubators, this time at 2.5L per tray. This lesser number of eggs is used to allow for sufficient room once the alevin emerge. They will need more space and oxygen than developing eggs.

Rather than manually picking out the dead and infertile eggs by hand, a device called a Jensorter is used. A rotating wheel with a series of holes along its perimeter picks up the eggs from a reservoir and by means of a sensor and compressed air, bad eggs, which are white (see here for an example) are separated from the good. It is possible to sort about one hundred thousand eggs per hour, greatly diminishing the time that would have been required to remove the bad eggs individually by hand with forceps. This must still be done after the Jensorter has done its work since some bad eggs are ejected together with the good ones.

The Jensorter works by passing a beam of light into the egg as it passes over a sensor. If the egg is clear, it proceeds to an area where a burst of compressed air ejects the egg into the appropriate chute. If the egg is white, the egg is ejected into another chute. The Jensorter cannot differentiate between a clear, infertile egg and one that is alive, since the opacity of the eggs is very similar. Therefore, hatchery workers shock the eggs so that infertile ones turn white so they are recognized by the Jensorter. Fertile eggs are quite robust at this stage and can be handled without damage, but the cell membrane of an infertile egg is relatively fragile and rough handling will cause it to be damaged and it will turn white. To achieve the physical handling needed to mechanically damage the infertile eggs, trays are emptied into a large tub and agitated by hand. After about 12 hours, eggs so treated become white and will be detected and rejected by the Jensorter. After running through the Jensorter, the eggs are returned to the incubation trays where they will remain until they reach the free-swimming stage.

Andy Rubaszek
Ringwood Fish Culture Station
andyr@sympatico.ca