Red fish: Why are some fish in the Gulf of Maine red?

Monday, October 15, 2012 by Caroline Casals

Lets take a look at some red fish and other animals that live in the Gulf of Maine.  

American LobsterNorthern shrimp trawlDeep sea spider crabAcadian Redfish

Animals use their skin colors to blend in, but the ocean definitely isn’t red!  So what on earth are these little fish doing?

 Acadian Redfish

Acadian redfish, Sebastes fasciatus. 

In order to answer this question we have to understand a little about how color works.  We need light in order to see color, and white “normal” light is made of a whole bunch of colors, that’s what a rainbow is!


            The colors that you see on your shirt, your car, or on your pet fish are all made by the colors that bounce back.  So your blue tee shirt looks blue because when all of the colors in that white light shine on it, only the blue light bounced back to your eye.

            So what happens to a red fish when there is no red light to shine on it?

In the ocean, the different colors in that white light get absorbed, or blocked, pretty quickly. 

 Seawater light absorption

In this picture we can see that red light gets absorbed first and only makes it a few feet deep.  Green light goes a little farther and blue light goes the farthest.  Our red fish might look red to us up here, but what about deep below the surface of the ocean under only blue light?  Fortunately we don't have to hop in a submarine or go SCUBA diving to test this (on second thought, that sounds like fun), all we need is a box where no outside light gets in and for our experimental light we can use different color LEDs....

Cardboard shoeboxTri color LED prototype

(science sometimes involves carboard and batteries)

All we need now are some fishy volunteers:

Swedish Fish

Brave, brave fish.  Putting it all on the line for SCIENCE!

Lets see what our light box experiment shows...

 Swedish fish RGB light 

Red fish under white light (red, green, and blue light)

Swedish fish GB light

Red fish under blue and green light only (with a green sour patch kid snuck in)

Abracadabra!  Our red fish looks black under blue light.  In the deep ocean there is very little light and most everything looks dark and black, including our red fish.  Pretty cool huh?  This means that our red fish lives his whole life in deep water, and near the bottom (read about the silver fish to see why) so predators won’t be under him very often.  These fish that live near the bottom, but not glued to it like the flat fish, are called dimersal fish.

Do you have any animals or plants at home that use unusual hiding stratigies?  **Bonus** How do other sea creatures adapt to deep oceans other than unusual colors? Let us know in the comments below!

Learn more about brown fishsilver fish, or go back to the start.

Photo credits:

Splash image: NOAA.  All others, top to bottom, left to right: NOAA, Aldric D Eon -- NOAA, Jeff Pollack -- NOAA, Sea Grant (NOAA), Steven G Johnson,, NASA, -- user Jiffy, Hunterseeker Armory,, (last two) Caroline Casals. 

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