Why Are My Eggs Hatching Early?

I have received several inquiries regarding eggs that are hatching seemingly early. A few teachers have reported eggs hatching before they even made it into the fish tank. As sponsor, you may be the first point of contact for teachers.

All in all – we are experiencing a successful year. The eggs are healthy, we are seeing good survival rates, and most of all – students are learning about fish and aquatic habitats. Yes, some classes have to change their release date to accommodate early hatch and fast development.


Here are a few insights:

  • Hatching fish in classrooms is not an exact science – there are some variables we do not control.
  • The water at the source hatchery fluctuates based on weather. The temperature I give you (and which is recorded on the 772 permit) is an average, not a constant. February had some warm days and this may have impacted the development of the eggs.
  • The eggs will develop at different rates both at the source hatchery and in classrooms. The eggs are addled (shocked) at the hatchery when a large percentage of the eggs have “eyed” and again, some will be further along the process and others a bit behind.
  • The eggs we use have undergone a process to sterilize the eggs to keep the fish from being able to reproduce. This is a new process for CDFW and for most fish hatcheries in general. It appears that triploid (sterilized) eggs develop more rapidly than do diploid (fertile) eggs.

Please keep in mind that this is an educational program on what fish need to survive. There are aspects to the process we simply do not control. This alone is a good topic for conversation with students – the fact that humans attempts to control nature have not always worked out as we had originally envisioned. For example, 60 years ago we built dams to store water and protect against floods. To mitigate the loss of habitat, hatcheries were built to make up for lost habitat. Today we find that hatcheries alone are not enough to maintain anadromous fish populations and the old models for having adequate water storage to protect against floods may not be sufficient. More than a century ago we saw burning of fossil fuels as the path to development and progress and now we face issues that may be related to the excessive burning of these fuels.

Interestingly, not all tanks are experiencing this early hatch. There is a bit of variation around the bay area despite the fact that most tanks are running at similar temperatures.

For next year, we will see if we can get eggs that are a couple of days “younger” into classrooms.

If you have questions, please let me know. You are doing a great job and if the eggs hatch early, it is not because you are doing something wrong. Sometimes we are less in control than we like to think we are.

About Ethan Rotman

Ethan Rotman (Bayareatic) manages and coordinates programs that hatch fish in classrooms for the San Francisco Bay Area. He also chairs the committee that manages these programs throughout the state. Ethan has worked with the California Department of Fish and Wildlife for over 20 years.
This entry was posted in Uncategorized. Bookmark the permalink.


Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s