The Colors of California Squid

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	The Colors of California Squid

Squid can not only be incredibly colorful, as this picture shows dramatically, but they can also change color to blend in with their surroundings. How do they do that ?

Why Squid Change Color

Squid skin is translucent. Color comes from pigment cells, called chromatophores, located in the outer layer of skin. These chromatophores appear as small patches or dots. Chromatophores in California market squid contain red, yellow, or brownish-black pigments.

Model of the Sepioteuthis Chromatophore

[1] Muscle fibers expand and contract the chromatophore

This is a simplified example of an actual pigment cell in the squid dermis. Think of the pigment cell in the chromatophore as a flexible bag of color. It can be stretched out to cover a large flat area or retracted back to a small, retracted point. The cell is attached to 30 radial muscle fibers at various points along the edge in a relative plane parallel to the skin surface. These muscles are in turn controlled by a nerve fiber. When a nerve impulse travels to the muscles, it causes the muscles to contract. The muscles pull in different directions and expand the cell. Relaxng the muscles causes the cells to return to a smaller and more compact shape, thus reducing the area of the chromatophore, and making the pigmented area shrink.

[2] As different patches expand and contract, the skin of the squid changes color

In squid, different colored chromatophores are controlled by different nerve fibers. This allows the squid to selectively retract or expand sets of chromatophores and increase or decrease the amount of a selected color. For example, by retracting all of the black pigmented cells, the squid will appear to suddenly lighten. By expanding the red chromatophores, as Loligo may do when excited, the animal will flush with a deep red. The sudden retraction of all the chromatophores (as seen in the illustration) has the net effect of reducing all the colors, and the squid appears to fade into the water column.

After N Caloylanis and C Berger, Marine Biological Laboratory, Woods Hole, MA 02543

Judging Squid Freshness by Color

The bright colors of live squid, fade after the squid is harvested, as this sequence shows.

30 seconds after harvest

California squid are harvested with round-haul nets and pumped from the sea across a dewatering screen and into a hold containing refrigerated seawater. In this photograph, the squid are less than 30 seconds out of the water. These squid exhibit the natural color variation seen in freshly harvested California squid.

5 minutes after harvest

Squid die quickly after harvest. These squid were photographed minutes after harvest, and illustrate the natural color variation present in California squid. After death, squid coloration slowly fades, but the colors do not change.

1 day after harvest

When squid are unloaded from fishing vessels, they are immediately transferred into bins containing ice water. Squid are soaked in ice water for a few hours until they are processed. These squid, photographed 24 hours after harvest, show the bleaching effect of the ice water, but also show that squid retain some of the natural color they had when harvested.

3 days after harvest

California squid held at 4 ° C (40 ° F) for 3 days after harvest retain some of their natural color and continue to show some color variation. The top (dorsal) view of the squid appears brownish in color, the ventral view (underside of squid) is reddish in color. When the skin is removed (bottom picture), the squid meat appears nearly white, without discoloration.

6 days after harvest

California squid held at 4 ° C (40 ° F) for 6 days after harvest retained some natural color variation. The squid meat still appeared white, although a slight off-color odor was present due to enzymatic breakdown of the squid viscera and muscle.

10 days after harvest

California squid held at 4 ° C (40 ° F) for 10 days after harvest retained some natural color variation, but the skin appeared slightly reddish-purple in color. The meat of the squid was mostly white with some red to purple discoloration. The odor of the squid was strongly putrid.

Poor quality squid have a dark red or purple discoloration of the meat, and a strong off-odor.

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