April 30, 2020, by Kristina Tirman

At the Science Center, we are able to closely observe some of the stages of the salmon life cycle – spawning adult, eggs, alevin, and fry.  In the fall, spawning adults return to the hatchery, eggs are saved, fertilized, and incubated in incubation trays for the next several months.  Finally, in early winter, pink and chum young emerge from the eggs and are called, alevin.  They carry their food with them in a yolk sac.  Because they have this weighty lunch box attached, alevin are not very buoyant and stay at the bottom of the incubation tray just like they would do in the gravel of a stream.  Only later, when the yolk sac is absorbed are the alevin able to push themselves to the surface of the water to gulp some air to fill their swim bladder.  The swim bladder provides buoyancy. 

Look at the photos of alevin and watch the videos of the early swimming fry and then, the net pen fry to observe the differences in each of these growth stages.

Once you’ve watched the videos, download the Science Bite worksheet to answer some questions about these important life stages!