Collecting and Fertilizing Eggs

PWSAC updated the egg-take systems at AFK, CCH, and WNH with electroanesthesia technology and mechanized the system.  This has increased the efficiency of the operation (more eggs per hour, less manpower) and eliminated the wear and tear on hatchery technicians by reducing the handling of live adult salmon.

The top left picture shows the CCH egg-take raceway where a fish culturist is operating the hydraulic raceway crowder, fish lift, and electroanesthesia unit.  This egg-take step took a total of nine people with the old system.  The top right picture shows the operation of lifting the fish out of the raceway and into the electroanesthesia unit.  Once the fish are anesthetized they slide into the egg-take room through an opening in the wall just past the window.  Another person (lower left picture) then sorts the fish by sex.

Once in the egg-take room and sorted, the fish slide to one of four fish culturists who extract the gametes as shown in the lower right picture.  The eggs and sperm slide into a common trough that empties into a single bucket.

Fertilization of the eggs occurs once water is added to the bucket in the rinse tank activating the sperm.  Fertilization is instantaneous but the fish culturists allow the eggs to stay in contact with the milt for 30 seconds just to make sure.  The excess sperm, ovarian fluid, and blood are then rinsed and the eggs are gently poured into the incubator.

Incubating the Eggs

Egg fertility samples can be taken approximately 10 hours after fertilization depending on the temperature of the incubation water.  The left picture shows a fish culturist examining the blastodisc of an egg (white spot).  A fertilized egg will have a developed blastodisc that will have divided into four cells looking somewhat like a shamrock where an unfertilized egg will have a blastodisc that will be a smooth circle.  Fertility sampling during the egg-takes acts as a quality control measure giving the hatchery managers feedback on the success egg-take operation.  Typical pink salmon egg-take fertilities range from 95-100%.

The natural stream environment is mimicked in an incubator by the constant upwelling flow of fresh water which supplies oxygen and washes away waste.  Often, incubator trays are filled with small, plastic, saddle-shaped pieces that act as artificial gravel (called substrate).  The substrate provides hundreds of thousands of hiding spaces where the alevin may remain undisturbed, absorbing their yolk material for body development.  The right picture shows an incubator with pink salmon eggs at CCH.

The salmon embryos continue to develop in the eggs into the fall months.  The pink and chum salmon eggs reach the “eyed egg stage” starting in October.  At this stage, a distinct eye is visible through the egg shell and the early formation of otoliths are under way.  The otoliths are part of the salmon’s inner ear equilibrium system.  Otoliths are made up of protein and calcium carbonate which grows from the inside out, much like the rings of a tree.  The pictures above are a cross-sectional view of CCH and WNH pink salmon from the 1997 brood year.  The white area is the calcium carbonate and the dark rings are the protein layer.  By manipulating the incubation water temperature, fish culturists can induce protein rings at regular intervals (otolith marks) that look somewhat like a bar-code.  This can be done in mass to 100% of the population.  This is an extremely valuable fisheries management tool as the adults return into a mixed stock fishery (hatchery fish are marked and natural stocks are not).  The picture on the left is a CCH pink salmon indicated by two bands of comprised of three rings each ( ||| ||| ).  The picture on the right is a WNH pink salmon with one band of eight rings ( |||||||| ).  For more information on otoliths and/or otolith marking visit our friends at the ADF&G Otolith Lab.

Between November and January, the fish hatch out of their eggs and are called alevin (fry with yolk sacs attached).  The alevin continue to develop using the yolk material for growth.  During this period, the young salmon are very sensitive to light, so the incubation room is kept dark as much as possible.  By March, the alevin have absorbed most of their yolk sacs and their bellies have “buttoned-up.”  At this point the fry begin to emerge from the incubation substrate.  The fry leave the incubators (outmigration) begining in late March and extends into May.

Feeding the Fry

After the fry emerge from the incubators they are, depending on their species and hatchery program, either are directly released into local waters, or held in captivity and fed a commercially manufactured fish food.  Often, fry are moved to saltwater rearing net pens and fed prior to release.  The fry imprint to the various chemical characteristics of the surrounding environment.  It is this imprinting process that enables the fish to instinctively return to their release site as mature adults to spawn.

Several factors determine how long the fish are fed in the net pens before they are released.  In order to increase the survival rate, a key target size and release time is selected.  But often, critical factors, such as the occurrence of “zooplankton blooms” in the receiving waters which will provide natural feed for the fry upon their release, also influence the decision as to when to release the fry.

Long-Term Rearing

The fertilization and incubation process of culturing the five species of salmon are basically the same.  Pink and chum salmon are biologically adapted to living in saltwater immediately after they have emerged from incubators.  However coho, sockeye, and Chinook salmon must remain in freshwater for an additional year until they have reached a stage of development known as “smolt”, which allows them to physiologically adapt to saltwater.  Because these smolt have been reared for sometime in freshwater, they are bigger than pink and chum salmon fry and generally have a better chance of surviving in the wild and eventually returning as adult fish.  Some coho and Chinook salmon are released remotely (away from the hatchery) for the sport fishery.

Returning Adults!

A major phase of a PNP hatchery operation is to “harvest” a portion of the returning adults for broodstock or licenses a portion of the returning salmon for a fee to seafood processors who in turn catch and sell the fish “cost recovery.”  The picture on the left shows a seiner making a set in front of the AFK hatchery brood enclosure.  The cost recovery fish are pumped directly from the seiner’s net onto a processor’s tender (right picture).  During the harvest period, fish culturists sample the harvested adults for average weight, sex ratio, and stage of maturity.


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