Dabbling in the mysteries of fish colorations and shadings

Brian Van Acker raised a question about fish colors that I receive regularly in some form.

‘‘I caught these two channel catfish [on a June weekend] in two different bodies of water,’’ he tweeted. ‘‘The first was 25 inches, 7 pounds; the second was 24 inches and guessing 5 pounds. Their colors are very different. What would cause this? Different bodies of water? Age of the fish?’’

Chris Taylor, a Ph.D. and the curator of fishes and crustaceans for the Illinois Natural History Survey, emailed: ‘‘The light-colored fish [at the top] might actually be a white catfish, while the darker one [below]is a channel catfish. White catfish are not common in Illinois and not native to the state. They were stocked in various locations over the last five [years].’’

As to the broader question of fish coloration, Taylor emailed: ‘‘Fishes use coloration for two main purposes: communication and evasion from predators. To your question about why do some individuals of the same species have different colors in Illinois species, it’s mostly due to communication. In most species, the males have the more prominent colors, and those males use those colors to increase their attractiveness to females. Just like a lion with a large mane is more ‘fit’ to be a mate, the more brightly colored male fish is more fit. The male coloration is also used to notify other males that they are the ‘top dog.’ In a lake full of fish, there will be a wide range of sizes and health (fitness) in males of a single species.

‘‘That said, you were also correct in stating that depth and habitat can alter coloration a bit. Less light penetrates to deeper depths, and water clarity in a large [body of water] or stream can vary. Depending on depth or clarity, fishes may need to increase or decrease the intensity of their color to get noticed.’’

I also asked about how fish change colors. Put on your science hats for this.

‘‘This gets complicated very quickly, but in a nutshell fishes have cells called chromatophores near the skin surface that are very irregular in shape,’’ Taylor emailed. ‘‘Different color pigments (reds, greens, yellows) occur in the chromatophores, and these pigments are very small. Either by using hormones or nerves, fishes can either accumulate the pigments in a small, tight cluster within the chromatophore to lighten that color, or they can spread out those pigments across the chromatophore to increase the intensity of the color. The hormonal control of coloration can cause color change that may last for months. This is why breeding males look different from non-breeding males.

‘‘One last point is that body size can impact coloration. Larger individuals can have more pigment and, hence, darker or brighter colors.

‘‘Color change caused by nerve function usually happens quite quickly and usually involves darkening of various areas of the body. For example, the sudden appearance of a predator can cause fishes to quickly darken body sides to help them become more cryptically colored and blend into background areas or vegetation.’’

Wild things

Chris Strand encountered his first river otter Saturday while fishing the Des Plaines River. ‘‘To be honest, it looked like a Loch Ness Monster!’’ he messaged. ‘‘Lol. The way its head, then body, then tail snaked in the water, I see how people make the mistake.’’ . . . I couldn’t find hen-of-the-woods mushrooms Friday, but I did find chicken-of-the-woods.

Stray cast

Bears season already feels like your boot slipping on a rock while crossing a stream.