What Determines the Color of Fish Flesh?

White fish, red fish, and even blue fish! Fish flesh comes in a wide variety of different colors, but what is responsible for this variability?

The color of fish flesh is impacted by a wide variety of different elements including environmental factors, activity levels, diet, species, and much more.

In this article, we will give you an overview of everything that can impact the flesh color of a fish and how the packaging and storage process may also affect its color.

One major determinant of fish flesh coloration is the fish’s activity level. This is all thanks to a protein called myoglobin.

Myoglobin is responsible for storing oxygen in a fish’s muscles and it has a dark red pigment. Fish flesh (meat) that is red is made up of muscles that are very active and therefore require a lot of oxygen. Therefore, they contain a lot of myoglobin which adds the red color to the flesh.

Since fish float and do not require constant energy to support their skeletons, most fish flesh is white. Even in white flesh fish there will usually be some red meat around the fin or tail which is used for swimming. Alternatively, fish that swim long distances, such as tuna, need more oxygen flowing through their muscles and therefore tend to have red flesh.

You are what you eat or at least that’s true when it comes to fish flesh colors. Ever wonder why some fish such as salmon have pink or red flesh? That’s because those fish tend to feed on crustaceans such as shrimp and krill.

Crustaceans contain reddish-orange pigments called carotenoids. The fish's flesh takes on the color of these carotenoids. Different salmon species tend to eat different proportions of these crustaceans, which is what causes the different hues across species. The process is slightly different for farmed fish. Farmed salmon and other farmed fish with pink flesh such as arctic char don’t have access to wild crustaceans. Typically astaxanthin, a naturally occurring compound in carotenoids, is added to the feed to create the pink flesh you see.

Fat content also impacts the color of fish flesh. Fish cannot synthesize carotenoids and therefore absorb the pigmentation through the food that they eat. If fish do not have a high enough level of fat, then they are unable to absorb the carotenoids. This is one reason why fish with lower fat content tend to have white flesh.

While a fish’s environment is not the largest contributing factor to the color of its flesh it does have an impact. Some environmental factors that influence the flesh color are temperature, population density and saline levels. Pollutants can cause variation as well.

Although it is extremely rare, some fish can occasionally have blue flesh. This is caused by a bile pigment called biliverdin that turns the fish’s blood serum blue. The blue color will dissipate once the fish is cooked. Biliverdin is also the pigment responsible for the bluish color sometimes seen in bruises.

Fish that can have blue meat include lingcod, rock greenling, kelp greenling and cabezon. While their flesh can turn blue, they typically have white flesh.

Some other rare examples of meat colors in fish are orange swordfish (often called pumpkin swordfish), which comes from a diet rich in shrimp and white king salmon, which is caused by the inability of some salmon to store carotenoids in their muscle cells.

Now that we’ve discussed all of the ways that fish flesh can change naturally, let’s look at the ways that the storage and preparation of fish can impact its flesh color.

Freezing darker flesh fish like salmon or tuna can cause the color of the fish to dull.

Freezing white fish like haddock or pollock can cause the middle brown muscle of the fish to become more pronounced.

As fish ages, it begins to lose its natural color. A lot can happen to affect the fish’s flesh color during the process of getting it from the ocean to your kitchen.

If a white fish is canned or frozen in poor conditions, it can start to brown. Additionally, if the fish is processed using heat (or is exposed to heat) it will turn brown as well.

Red and orange fish will begin to dull over time. The color of the fish can be an indicator of its freshness; however, some seafood companies use industry tricks to make fish appear more vibrant and visually appealing.

One of these tricks is commonly used to restore tuna to a more vibrant red color. Exposing the meat to carbon monoxide gas will make tuna a luscious red. While this is illegal in some countries, it’s still a practice used in the US.

At Fulton Fish Market, our products are the freshest you will find other than catching it yourself and our frozen products are frozen quickly after catch. We never use gas to alter the color of the flesh.

Have you ever noticed that fish meat turns a different color during the cooking process? The following types of fish change color when you apply heat to them:

• Halibut goes from translucent to white.
• Tuna changes to a lighter color.
• Salmon goes from red/orange to a soft pink.

The reason that fish change color during the cooking process is the result of the coagulation of proteins. The cooking process will cause the fish meat to become denser as a result of coagulation as well.

While a more vibrant color can indicate a fresher fish, it’s not the only factor in play. Therefore, it’s important to buy fish from a reputable company that you can trust instead of solely relying on the coloring of the fish to determine its quality. To get the best quality seafood, buy your fish from a company like Fulton Fish Market that delivers fresh fish in a timely manner.