Published on Feb. 27, 2020

Incubator hatch comparison

Abstract: To determine the production advantage in four various methods of hatching eggs of Rainbow Trout. Each method to be describe in full detail, data collected throughout trial, and key findings recorded to determine which, if any, is the most efficient method of incubating and hatching eggs.


Different types of incubators exist in commercial trout farming. Primarily, heath stack incubators, and hatching jar incubators. The function of each is the same, to bring eggs from the eyed stage to hatch, but the hydraulics and environment experienced by hatched fry varies by incubator type. The different environment experience by the fry post hatch could influence stress levels, energy expenditure and overall health.

We test this by comparing hatch and ponding parameters of the two different incubator types. One type is the standard upwelling jar, sometimes referred to as a McDonald Upwell. The other type is a vertical stack system, often referred to as a Heath Stack. Within the vertical stack system, we will try three different types of media. Types of media are described below.


Eggs Used

Eggs used in this trial were from a standard production lot of the August spawning population supplied from the Trout Springs facility in Sumner, Washington. Upon reaching approximately 210 accumulated temperature units (ATUs), eggs were processed to remove dead and underdeveloped eggs, then boxed and shipped to the Rock Creek facility in Twin Falls, Idaho.

Upon arrival, eggs were randomly divided into eight batches of 4000 eggs each. Each batch of 4000 was placed into one of the four different incubator types described below. This allowed for two replicates of each incubation device. The eggs were set into the different types of media using a 32oz beaker for transferring. Flow was added to the systems at approximately 6 litres per minute. Black Plastic was used to wrap the upwelling jars so that no ambient light would influence the eggs.

Incubator Characteristics

Vertical Flow Stacks

Widely used and commercially available systems that utilize a gravity flow design to incubate eggs. These stacks typically come in 4-8 tray systems but can be stacked on top of one another depending on water quality and flow. They are more often being utilized by state agencies and for research purposes, as they can easily separate small numerations, as well as different types of eggs, in the same system. Often referred to as a Heath Stack, these stacks provide professional breeding and hatching of salmonid eggs and can be combined and arranged in different ways, to utilise the availabe space as effectively as possible. The water from the inlet, flows through the trays on which the eggs stay, and leaves the water tray over the front, through the side canals, to the next tray, were it flows again through the egg tray and so on, so that all trays will be supplied with sufficient water. Without disturbing the other trays, each tray can be drawn out and controlled easily and provides perfect conditions from the fertilized egg to the swim-up stage.

Substrates for Vertical Flow Incubators

Several different types of substrates are being manufactured for the vertical flow incubation systems. The reasoning of these various types of substrate is that by separating the eggs using the media, there will be less spread of fungus, less energy expended from newly hatched alevins, and improved flow throughout the tray. The hatching substrate imitates the gravel substrate naturaly occuring in the brooks or rivers and provides optimal developmental conditions for the fish larvae. The fry are theroretically stronger and healthier, also would have less deformations and lower mortalities, and improved growth.

Heath Stack:

  • Open Tray ( C ) :
      • Even water flow with places for fish to hide away from current
      • Water is used in series from top try to bottom tray
      • Environment is dark and eggs/fry are protected from light even if lights are turned on.

  • Tray with Substrate Insert ( DI ) :
      • Same as above, only with increased area for fish to hide away from current.
      • Substrate removeable

  • Tray with Substrate Built In ( BI ) :
      • Same as above but media is not removable

Hatching Jar

The most used method of incubation, worldwide. Water is forced to the bottom of the incubator and then flows up through the eggs and out of the system. There are several known issues with this system such as, uneven flow, unknown stocking densities directly related to egg size, and fungus control. The most difficult aspect of using this system is acquiring accurate measurements of mortality and stopping the spread of fungus. Also known as McDonald Upwell.

Hatching Jars ( J ):

    1. Upwelling water – provides slightly more turbulent environment
    2. Single pass water
    3. Fry are exposed to full light unless ambient light is off.

hatching trial.png

Figure 1: Overall Project Design- showing the different incubations systems used in the trial.

Example of Substrate

hatching trial - substrate1.jpg

hatching trial - substrate2.jpg

Water Conditions:

  • 13.20 C
  • Spring Water
  • First Use
  • Fed to apparent satiation on Skretting classic starter Crumble #0 to 0.8g, then #1 to end of trial

Data Collected:

  • Hatch Survival
  • Daily Mortality
  • Degree days between peak hatch and full yolk sack absorption
  • Degree days between peak hatch and first feeding
  • Weight of fish at first feeding
  • Degree days between peak hatch and 1g avg weight

Results and discussion

From the results we can conclude that different incubation medias did not have a significant effect on overall survival at these low stocking densities. Similar mortality was observed in all systems, with no clear advantages to any one method. It should be noted that mortality was much easier removed and maintained in the Open Tray Control ( C ) system, compared to all other systems. Staff found both the Built In ( BI ) and Drop In ( DI) substrates to be difficult to use. They did not allow for proper cleaning, fungus developed underneath the substrate in the Drop In system (DI), and flow did not appear to be even throughout the tray.

Length of time between peak hatch and first feeding was similar in all groups, averaging around 170 ATU. Peak Hatch defined as more than 75% of the total group having fully hatched. (See Table 1 below)

Weight of the fry upon first feeding was noticeably less in the jar incubation system, compared to all vertical stack methods. We believe this to be the direct result of the amount of energy expelled in the jar system to maintain upright position and combating the required flow to the jar.

The control group reached 1 gram average weight at 765 ATUs. This was a 14% larger fry than our Jar group. From this we can conclude that the alevins are expending more energy in the jar and have a decreased efficiency once they are moved to an open water system.

Group Avg Wt. 171.6 ATU Avg Wt. 765.6 ATU % Survival to 765.6 ATU % difference to control at 1g av wt
First feeding 1 gram average
C 0.115 1.02 88.71
J 0.097 0.88 88.41 -14%
BI 0.112 0.96 89.33 -6%
DI 0.113 1.01 89.23 -1%

hatch trial - graph avg wt first feeding.png

Avg. Wt. @ 170 ATU (first feeding)

hatch trial - graph 1 gram average.png

Avg. Wt. @765 ATU (1 gram average)

Figure 3: Graph showing weights of Alevins at first feeding and at 1g

Summary and conclusions

From this trial we can conclude that the Hatching Jar incubation method has a negative impact on fry weight and early life stage growth. This early growth is crucial for the overall success and health of the fish throughout their full life cycle. Substrates in this trial, did not seem to have noticeable advantages, and proved to be restricting normal hatchery procedures such as cleaning and data collection. Recommendations of future trials would be to continue tracking size to 100 grams, and reducing group numeration.

It should be keenly noted that the tray incubation systems offer a considerable advantage to 1g which will have a significant impact on the length of time to target size in the hatchery and subsequent grow out.

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