Are Catfish Colorblind? NO!

The Color Preference of Catfish

by

Caitlin Young

8th Grade

Muller Road Middle School
Blythewood, South Carolina

    My experiment is on the color preference of catfish.
    
Discussion
    Most people think that catfish only feed by touch and smell and are not visual feeders. But this is not entirely true; most catfish have at least adequate eyesight. All catfish are highly evolved creatures, with complex senses. Channel catfish, in particular, have good eyesight and are known to be very visual feeders under the right conditions. So, I decided to put that to the test.
    The common misconception is that catfish are lazy bottom feeders that eat only rotten, putrefied food that stinks. Supposedly, they find this disgusting buffet using only their whiskers and highly developed sense of smell. I thought it would be interesting to see if they might also utilize their eyesight to determine what they’re going to feed on.
    It’s already well known that the structure of the eye in many fishes is similar to the human eye. This is especially the case with freshwater fishese like catfish. Their eyes ususally contain rods and cones like our eyes, which allows them to pick up color. With this in my mind, my experiment was designed to answer two questions:

• Is color a factor to catfish in feeding preference?
• If color was a factor, which color triggers more bites?

    I did some background research and found the top four colors that catfish were rumored to like. Then I hand-tied a basic Wooly Bugger-style fly in those exact colors. The top four colors are:

• Black
• Blue
• Pink
• Chartreuse

Hand Tied Flies 

    Then I made a chart with three vertical columns and four horizontal rows. The rows were for the colors and the columns were for the number of trial tests I would run.

    Now, I needed some fish.

    I couldn't rely on the natural environment to provide these fish; it lacked control. And all science experimentation relies in the element of control.
What to do?
    Luckily, I found the Cohen Campbell Fisheries Center outside Columbia, South Carolina. It turns out they had catfish they use for stocking waters in the state. These fish are housed in tank that would be just the right size, with good water clarity. This allowed me to conduct my experiment under observable, controlled conditions. The people at the Campbell Center were also very accommodating, because, as far as they knew, no one had done a study like this on catfish. Other fishes like bass, yes.
But not catfish, specifically. 
    Many tests and studies have been done on scents and the catfishes sense of smell. But there is precious little concern about their eyesight. Some anecdotal information exists, but it is entirely unreliable. Ask four fishermen which color works best, and you’ll get four different answers.  Scientific studies, however, were in short supply.
    I decided to use science to prove once and for all which color catfish actually prefer. For all I knew, I could be the first to attempt this. For this reason, the folks at the Campbell center were keenly interested and placed their facility at my disposal.

METHOD: I would run each of the flies through the holding tank, a set number of times. I would then record the reaction if the fish to each color.

SUMMARY: At the end of the experiment, I learned that that catfish do, indeed, have a color preference. They overwhelmingly chose blue, which confirmed the hypothesis I will present later. Chartreuse was a close second, followed by black, with pink coming in last.

THE EXPERIMENT: This experiment uses four different colors of flies (hook removed) and each was tested with a group of catfish in a controlled environment.
Each fly is to be pulled through a tank containing several thousand catfish the same number of times. Each time a fish bites a fly, it will be counted.

THE HYPOTHESIS: My hypothesis is that IF catfish do have a color preference, then the color will be blue. This is based on the research that I did about the structure of the eye; I concluded that channel catfish not only “smell” their way to food, but are also visual predators. Their eyes respond mostly to greens and blues, because those colors reflect the most light under most water conditions.
My research also revealed that blue is the last color of the spectrum to disappear underwater, the deeper you go. And since catfish mostly inhabit the waters close to the bottom, I hypothesized that blue will be the color they see the most and so will be their favorite color.

MATERIALS:

• One fishing pole and reel spooled with four-pound-test clear monofilament line.
• Four flies that I tied myself.
  In an effort to ensure consistency, I tied one style fly only, in the following colors:
  one blue, one pink, one green, and one black.
• A 15’ x 10’ concrete holding tank located at the Cohen Campbell Fish Hatchery.
• Approximately 4,000 channel catfish (based on the count provided by the hatcher manager).
• A wire spreader bar with three attachments for flies.
• A tracking graph and a pencil.

METHODS: I tied four flies in the following colors; pink, blue, black and chartreuse. I cut OFF the hook points off so I would not hurt the fish, or slow down the process. I was only interested in the number of takes, or "hits," each fly would receive.

    The first thing I did when I got to the tank was tie a pink fly onto the fishing line and slowly pulled the fly through the length of a 15’ x 10’ tank 15 times. Each time the fly was hit by a  fish, I recorded it, and tallied the total number of hits for each run.
    I repeated this process two more times, for a total of three runs.
   Next, I repeated the entire process with each of the other three colors.
    I totaled all of the strikes for each color to determine the favorite color of fly the catfish preferred.

Caitlin Young performing one of her color tests.

VERIFICATION: After everything was totaled from the first tests, I verified the results with Part 2 of the test.

    For this, I employed a spreader bar, used to run THREE flies together at the same time. I put the least favorite color (pink) and the second leading color (chartreuse) on the outsides of the bar, and the favorite (blue) in the middle of the bar. This way, the fish would be forced to bypass the two brighter colors on the outside, in favor of the blue one in the middle.
    I made one run of 15 passes using the spreader bar and counted the number of times the fish targeted each color. I took the total number of strikes from the spreader bar test to either confirm or disprove my original findings.

PART 2 RESULTS:
    The pink fly garnered only 119 bites, and came in last place.
    Black was the second least favorite, gathering 137 bites. (Black is considered a "neutral" color. Most fishermen guessed that black would have done better than it did in my experiment.)
    Chartreuse again came in a close second, with 140 total bites.
    However, the blue fly was the overall favorite color with a total of 153 bites.

A helpful test fish

    My hypothesis was supported by this experiment. Even though my numbers confirmed that blue was the preferred color, the spreader bar helped to either confirm (or disprove) my original findings.
Even with the two brighter colors on the outside of the spreader bar, and seemingly easier to target, the fish still overwhelmingly targeted the blue fly. They hit the blue fly 21 times versus 10 hits on the pink and 13 hits for chartreuse. I was proven right that even with the two brightest colors on the outside, the fish would deliberately target the favored color in the middle.
    I was impressed, really, that even with the three flies so close together, the fish still went after the blue one. It would have been easier to bite either of the two flies on the outside, but they really went after that blue one. That really helped illustrate the color preference.

NOTES ON SCENT: I did one more test, apart from this experiment, solely out of curiosity.
     My presentation was designed solely around color, so I had to leave the element of scent out of the original experiment. But, since catfish are renowned for their sense of smell, it seemed useful to include something “smelly” in the experiment. Besides, I really wanted to see how much of a factor scent was.

    So I obtained some scented gel; Pro Cure’s “Nightcrawler Super Gel.”
I would use the blue fly, since it was the most popular. I tied a second blue fly as my control, and it would be UNSCENTED.
Then I ran them side by side, one with gel applied, and one without. Then, I counted how many hits each fly got.
    The results were overwhelming! The scented blue fly, took 135 hits, compared to only 36 for the unscented one. Then, again separate from my original experiment, I went back to the spreader bar and added the Super Gel scent to the outer pink fly.
    I left the unscented blue fly in the middle, and an unscented chartreuse fly on the other side. Surprisingly, the unscented blue fly outperformed even the scented pink one! That really convinced me just how much of a factor color can be.

CONCLUSION: My hypothesis was proven correct and backed up by the data from both the single runs and the run with the spreader bar. After researching how colors are seen underwater, it makes sense that blue would be the preferred color and they would react to it best.

1. Blue is the last color in the color spectrum to disappear under water.
2. Blue is also a color found on many of the baitfish that channel catfish feed on like herring and shad.        By putting three colors on one spreader bar only inches apart, I convincingly illustrated the fish’s preference for blue. Considering that blue remains visible, even in deep water, and after reviewing the validation of my tests, it seems hard to dispute my results.
    WE should also mention the second place winner, Chartreuse. Its appeal is understandable, since it is withint the spectrum of fluorescent colors, and is one the most easily seen colors under water. We have a saying here in the South - “If it aint chartreuse, it aint no use!” Apparently, that is not far from the truth.
    Why was pink such a dud? I can only surmise that, sinc pink is closely associated with red - and red spectrum colors are the first to fade under water.
    Black is a pretty neutral color, and many prey items are dark or black, its third place ranking is not all that surprising.

    After these tests, it seems obvious that catfish do actually have a color preference.
    This could change the way fishing companies develop and produce their products. In addition, it could increase sales in blue baits and flies. This kind of information can also help fishermen pick the right color when they’re fishing and increase the number of fish they catch. Fishing companies could also increase sales if the production of blue baits are increased and the public is made aware of my findings.
    There were no problems with my experiment, and everything went as planned. The people at Cohen Campbell Hatchery were fantastic to work with and very accommodating. My hearty thanks go out to them for their support.

Caitlin Young and the test tank for her research.

Sources

Uwphotographyguide.com: Underwater photography lighting fundamentals. “Which colors disappear first underwater?” Color spectrum by wavelength.

Scuba-tutor.com: Effects of water density on color and water absorption of color. Why some underwater photos seem washed out with blues. This is where I found that that the chart shows that reveals blue shades are absorbed last with reds being the first to be absorbed and disappear underwater.

Midwest Outdoors Magazine, June 2010 issue: “Does Color Make a Difference to Fish?” by Justin Hoffman.

Lane Hite, Hatchery Manager for Cohen Campbell Fish Hatchery.
PS: His own theory of color led him to choose the Pink fly.