A Fish of a Different Color

Photos courtesy of the IDNR Division of Fisheries.

Have you ever been fishing and noticed that the color of each fish is a little bit different? Maybe you regularly fish a few lakes in your area and have noticed that one of the lakes consistently produces golden-olive colored smallmouth bass, while the other two are chock-full of dark brown ones with stripes. Maybe you’ve even been one of the lucky few to catch a fish with a memorable complexion – an albino or one that is extremely bright. Fish are the most biodiverse vertebrates on planet Earth, so it is no surprise that they come in a variety of different colors and patterns. Snorkeling a coral reef would verify this, from clownfish to triggerfish, the whole spectrum can be found beneath the water’s surface. Although often appreciated, the purpose behind these visual displays is seldom understood. The color scheme that a fish expresses is far more than just eye candy to the devout angler, but an integral component of a fish’s ability to navigate life in a harsh aquatic ecosystem.

Coloration, patterns and their capacities to change play an important role in the life of fish, serving several functions. One key reason we see different stripes, bars, and patterns on fish is for camouflage purposes, which can make or break a fish’s ability to survive in its environment. Countershading, or the darkening of the upper portion of the body and lightening of the underside, is a commonly adopted color scheme that allows fish to blend in with their surroundings when viewed from above or below; a valuable asset for both predators and prey alike. Disruptive coloring, such as distinct markings or patterns, offers a similar service; breaking up the shape of a fish’s body to better blend into the environment around it and avoid being seen.

Coloration can offer more than camouflage, however, specific colors or markings can also send signals to others about mating potential, health and even social status. All fish rely on their coloration for one reason or another, and it is processes taking place at the cellular level that enable this.

Most of the work of color generation in fish comes from cells called chromatophores. Literally translated as “color bearers,” these cells are distributed across the skin of fish with the sole purpose of eliciting a specific color. The white light that we see around us actually contains different colors: red, yellow, green, blue and purple. When we see something of color, such as a red apple, the red color reflects back to our eye and all of the other colors are absorbed. A similar process happens in fish, but it is their chromatophores that can either absorb the light, known as a pigmentary color, or reflect the light, known as a structural color.

Pigmentary colors, from light-absorbing chromatophores, cause fish to appear black/brown, yellow, orange, red or blue. Structural colors, from the chromatophores that reflect light, either come across as a creamy white, as found on the underbellies of most species, or the iconic iridescent metallic sheen that shifts in the sun with the angle of viewing. The overall color that we see in fish is the product of a combination of different chromatophores working simultaneously, and, depending on the situation, can change over varying periods of time.

There are two types of color change processes in fish, both of which are prompted by a different set of factors. Chromatophores in fish can change slowly and over a long period of time, often referred to as ultimate color changes, which can be quite extreme. They generally develop between life stages and are strongly influenced by a fish’s genetics. An example of this being sockeye salmon changing from silver while they are in the ocean to their distinctive deep red coloration before spawning.

The second type of color change happens much faster, on a shorter time scale, and in response to environmental conditions, known as proximate color changes. The intensity of UV light, availability of resources, social status, or the need to adapt to a specific background, are all factors that could cause a fish to make a quick shift in color. For example, if you’ve ever fished in a tournament then you may have noticed that the fish in your livewell started to show more intense color patterns than the ones freshly pulled from the lake. The stress of being captured, paired with the dark environment of the livewell, stimulates the fish’s chromatophores to adjust color patterns. Thus, all fish will experience changes in color at some point in their life, however in rare instances, individuals can pop up that look drastically different than the rest of their species.

On occasion, the coloration of a fish can be atypical, extreme or just plain odd. Take for example the ‘neon pikes,’ being pulled out of numerous lakes in Canada, that have drawn attention in the fishing world for their bright blue throats and neon green mouths not typically seen in most northerns. Speculated as being a mutation, this radical color scheme is believed to result from a proliferation of chromatophores producing green hues that help with hunting near reeds or the water’s surface; a proximate color change that helps them blend into environments of lighter color.

Albinism, or the appearance of an entirely white fish, on the other hand, is a mutation in the chromatophores responsible for the colors black and brown. Specifically, a mutation in the chromatophore’s tyrosinase enzymes which results in a complete lack of melanin, giving them the ghostly appearance.

Not all cases of extreme color morphology can be attributed to a change in chromatophores, though. Blue walleye, not to be confused with the extinct ‘blue pike,’ are another hot topic at the boat launch. Genetically the same as the typical yellow walleye, the blue color of these fish is derived from a protein found in their surface mucus known as sandercyanin. The purpose of sandercyanin is debated, but it’s believed to provide photoprotection from UV radiation, as well as countershading benefits in the deeper waters that they seem to prefer.

Outside of mutations such as albinism, extreme color morphs exemplify the spectacular changes fish can experience in the pursuit of survival.

With a passing glance, it’s easy to appreciate a fish’s coloration as simply being attractive. Fish are often beautiful, but the mechanisms that drive coloration in fish are equally fascinating. So, the next time that you’re reeling one in, take an extra moment to admire the iridescence or any spawning colors that they may be showing. And if you happen to be so lucky to catch a rare color morph, such as a neon pike or a blue walleye, appreciate its unique adaptations and the layer of intrigue it adds to the world of fishing!

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Justin Lombardo is a graduate student at the University of Illinois with his research focused on angling and fish population dynamics. Although an avid fisherman, he has never had the pleasure of catching a rare color morphed fish.

Cory Suski is a professor in the Department of Natural Resources and Environmental Sciences at the University of Illinois. For almost 20 years he has conducted research on many aspects of fishing.