I read an article about how kokanee eat and I’m confused. What is a gill raker? And how does the food get from the gill raker into the fish’s stomach?

Answered by Gregg Losinski, Conservation Educator

First things first.   In Idaho, when we are talking about kokanee, we are actually talking about the same fish that we also call a sockeye salmon.   These are the fish that are famous for turning bright red when the time comes for them to spawn.  (Spawning is the way fish reproduce by laying eggs).

What is the difference between the two?  Simple, the kokanee is landlocked and never leaves Idaho, but if it somehow manages to leave and get to the ocean and eventually return then we call it a sockeye salmon.  So many sockeye salmon used to return to central Idaho they lent their name to one of our most famous lakes.   Redfish Lake got its name not just because the fish returned there, but in such great numbers that they used to make the lake look as if it were turning red!

Kokanee or sockeye salmon are zooplankton eaters.  This means that they eat some of the smallest creatures floating around in the water, who themselves graze on plankton; the even smaller organisms in the water that are able gather their energy from sunlight.  While zooplankton are to move around a little on their own, they are basically like tiny food pellets floating around waiting to be gobbled up.

The way kokanee and other fish are able to eat these tiny morsels is by cruising through the water and holding their mouths open so the water carrying the zooplankton goes  in and across tiny growths called gill rakers.  These gill rakers are sort of like the rakes we use to gather the leaves that fall in our yards. When kokanee feed it sort of the same as if you were to run around your yard dragging a rake, you would eventually end up with a rake full of leaves.

The cool thing about fish is that they are built to not only strain out these tiny critters to eat, but the gill rakers also form a funnel that flushes the zooplankton down their throat to be digested.   Most of the water passes back out throw the gills after the zooplankton have been trapped and basically rinsed down the drain.   At home you are able to stand at the kitchen sink and use the sprayer to rinse leftovers down the drain into the garbage disposal, but fish need to keep swimming to strain the plankton and rinse them down.

So while your parents might tell you to not eat and run, kokanee have to in order to survive!

Fish Gills

A fish’s gills are on either side of its head.  They are covered by a gill cover called an operculum.  To breathe, the fish opens it mouth, takes in water, then closes its mouth.  The water moves from the fish’s mouth, past its gills, and out from beneath the operculum.  As the water moves over the gills, oxygen from the water is absorbed into blood vessels in the gills through the process of diffusion.  

Diffusion experiment

Diffusion is the movement of molecules through a liquid or gas.

Materials:  bubble solution, dry ice, gloves for handling dry ice, glass bowl

Adult supervision is recommended for this project.

  1. Using the gloves, place a chunk of dry ice in the bottom of the bowl and add about 1/2 cup of water.  Wait about five minutes for the carbon dioxide gas to accumulate in the container.
  2. Blow bubbles into the container.   The bubbles will fall until they reach the layer of carbon dioxide and they will hover for a few seconds.  Slowly they will start to sink as the carbon dioxide diffuses into the bubble and replaces some of the air. Carbon dioxide is heavier than most of the other gases in air, causing the bubbles to sink. 

Leave a Reply

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 )

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