Home » News » Saltwater challenge: Getting salmon ready for smoltification

Saltwater challenge: Getting salmon ready for smoltification

It's not easy for salmon to make the transition to life in the salty sea. See how CIAA helps out from the perspective of a young fry.

by | June 15, 2023

salmon fry in a cooler full of salt water
Resurrection Bay sockeye smolt swim around in a cooler full of saltwater. This is their last test before they are ocean ready. Aly Crocker, CIAA

Smoltification is when a salmon fry begins to adapt to life in saltwater, but it can be a real challenge. To describe this process, let’s look through the eyes of a little fry named Nerka. 

Nerka’s journey begins

On a warm spring day at Trail Lakes Hatchery, an individual sockeye salmon fry, we’ll call Nerka, is developing an irresistible itch to flee to the ocean. However, this can be problematic when the ocean is miles away. Nerka needs to get to seawater. They don’t understand why, but the urge is irresistible. Hundreds of thousand of other sockeye fry have caught the same itch. 

Over the next few days, Nerka and their pals will begin the process of smoltification. Salmon fry beginning this process will be seen adapting at a slower rate, starting in freshwater and slowly moving into brackish water and eventually pure saltwater.

Nerka can’t ease into this new life stage as long as the hatchery keeps providing her a steady supply of fresh water. Nerka’s toughest challenge comes next. 

How hatcheries trigger smoltification

Trail Lakes hatchery staff use a process to find out when salmon are ready to smolt. It’s called the saltwater challenge, and it mimics ocean conditions before the salmon are taken to nearby ponds. Given the amount of salt and the need for cooling the water, it would be too difficult for the hatchery to fully simulate ocean conditions. This is why CIAA has chosen a simpler approach.

Nerka and 49 others will find themselves being scooped out of a raceway and placed into a large cooler, filled with a saltwater concentration of 30-35 parts per million. Using the cooler along with outside air temperatures, staff can make sure water temperatures hold steady within the range of one degree above or below true seawater temperatures at that time. 

Nerka passes the challenge

Nerka finds the water to be very satisfying; however, three others do not agree, unfortunately meaning the group as a whole has not passed the challenge. Time will pass and Nerka happens to be caught again and is now placed back into the challenge cooler with 49 other members. This time, only one member from Nerka’s group didn’t survive the five-day challenge. This is considered a huge success!

Trail Lakes crew quantifies this challenge as a pass when over 96 percent of fish survive the five days in mimicked seawater. Nerka belonged to the raceway group that contained the smallest fish while fish from the raceway with the heaviest average weights passed with flying colors. This means that Nerka and all others proved they are ready to move to the ocean. 

The saltwater challenge saves lives

The saltwater challenge ensures fish are ready to smolt prior to ponding, rather than just assuming they’re ready. By testing a small sample of fish at a time, we can limit how many fish die off by ponding these fish prematurely. Over the years, Trail Lakes staff has been adapting and learning this process, bringing ponding numbers over 97 percent survival from freshwater to saltwater.

You May Also Like

Upcoming Events

See Full Calendar →


Follow CIAA's monthly newsletter to learn more about local aquaculture.

We promise we’ll never spam! Take a look at our Privacy Policy for more info.

Follow CIAA on Facebook