Shrimp are decapod crustaceans with thousands of species worldwide, inhabiting diverse environments from deep-sea trenches to freshwater rivers. Given this biodiversity, there is no single answer to a shrimp’s color. The visual appearance depends on its species, diet, environment, and whether it is raw or cooked.
The Pigment Responsible for Color
The foundation of a shrimp’s color is astaxanthin, a reddish-orange carotenoid pigment. Shrimp cannot produce astaxanthin; they acquire it through their diet, primarily by consuming microalgae and zooplankton.
In a live shrimp, astaxanthin is chemically bound to a protein called crustacyanin. This pigment-protein complex masks the pigment’s natural red color by altering its light absorption properties. The concentration and binding method of this complex create the muted, non-red colors seen in raw shrimp, often resulting in blues, greens, browns, or grays.
Live Shrimp Coloration and Habitat
The visible color of a live shrimp is primarily functional, serving as camouflage to protect it from predators. The various hues are determined by the interaction between the pigment and protein. This color-changing ability is controlled by specialized pigment structures in the shell and tissues called chromatophores.
Species like the chameleon shrimp can shift their coloration to red, green, brown, or even become nearly transparent, depending on the algae they are hiding within. The density of the surrounding substrate also influences the final appearance. Shrimp grown on dark backgrounds typically develop a more intense coloration compared to those on a lighter substrate. Commercially harvested species, like white or brown shrimp, possess a dull, mottled grey or translucent body when raw, helping them blend into sandy or muddy seafloors.
In deep-sea environments, where blue-green light from the surface is minimal, many shrimp are a deep red color. This seemingly bright color functions as perfect camouflage in the dark depths. Red light is absorbed quickly in water, making the shrimp appear black to predators.
Why Shrimp Turn Red When Cooked
The shift from raw, muted colors to the familiar pink or red of cooked shrimp is the result of protein denaturation. Heat breaks the chemical bond between the astaxanthin pigment and the crustacyanin protein. This heat causes the crustacyanin protein structure to unwind and change shape, releasing the astaxanthin.
Once the protein is denatured and the pigment is freed, astaxanthin reverts to its natural, heat-stable reddish-orange color. This explains why nearly all shrimp species, regardless of their raw color, turn a shade of pink or red when cooked. The intensity of the final cooked color is directly related to the amount of astaxanthin the shrimp accumulated from its diet.