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Fish vision

post #1 of 11
Thread Starter 

Very...very interesting

Research throws light on fish vision

\t\t(July 16, 2007) Andrij Horodysky's research can be summed up in a simple saying—what you see is what you get. \t\tHorodysky, a VIMS graduate student working with faculty members \t\tRich Brill, \t\tRob Latour, and \t\tJack Musick, is using electroretinography— \t\ta technique first developed for studying human vision—to explore how fishes see the underwater world of Chesapeake Bay.
\t\tBrill, an internationally recognized fish physiologist, has recently turned his attention to the sensory world of fish and other marine organisms.
\t\tThe research is part of an emerging field called "visual ecology" that promises to throw new light on animal behavior and \t\tthe interactions between predators and prey. Horodysky and his advisors are pioneers in applying this field to Bay fishes.
\t\tThe researchers are focusing their initial studies on recreationally important Bay species such as \t\tstriped bass, \t\tweakfish, \t\tcroaker, and \t\tdrum. \t\tThis reflects the source of their funding, which comes from the \t\tRecreational Fishing Advisory Board of the \t\tVirginia Marine Resources Commission. The Board uses money from Virginia's saltwater fishing license to fund projects that improve the Commonwealth's recreational fisheries.
\t\tHorodysky also benefits from collaborations with Charter captains like Steve Wray, who provide him with the fish he needs for his experiments.
\t\t \t\t \t\t\t\t \t\t\t\t \t\t \t\t\t\tThis graph shows early results from Horodysky's \t\t\t\t\t\tfish-vision experiments. The width of the black bar shows the \t\t\t\t\t\tvisual range for each fish species; bar thickness indicates peak response to specific colors. \t\t\t\t\t\t Click image for larger version. \t\t\t\t \t\t\t\tHorodysky's preliminary results provide basic insight into how Bay fishes see the world. The results show that some species, like striped bass, are adapted to see large, swiftly moving prey in daylight. Others, like weakfish, are adapted to see small, sluggish prey at night.
\t\tHe is also comparing the types of prey that fishes are adapted to see with the prey items that are actually in their stomachs— \t\twith some surprising results that could hold important implications for fisheries management in coastal waters.
\t\tHorodysky's research shows that striped bass are most sensitive during daylight hours to a wide range of colors from blue to red, with a peak at chartreuse. They have a "flicker fusion frequency" (essentially the "shutter speed" of an eye) of around 50, relatively fast for a fish, which allows them to track large, quick-moving prey like menhaden.
\t\tCompared to striped bass, weakfish have slow vision (around 25 cycles per second) and are more sensitive to contrast than color. This allows them to see best under dim conditions, just right for detecting the small fish and shrimp that prowl the nighttime Bay. They also have the unusual ability to see in ultraviolet.
\t\t"Even though these two predators may swim side-by-side, they exist in different visual worlds," says Horodysky. "You've got two animals that are competing for the same food. How do they do it? Stripers use color to see and feed during the day. Weakfish use contrast sensitivity to see at night."
\t\tFor the most part, study of stomach contents by VIMS researchers confirms what Horodysky's vision research predicts. Work by Dr. Rob Latour shows that the stomachs of weakfish are largely empty during the day, and then quickly begin to fill with small fishes and shrimp as evening falls. Work by graduate student Kathleen McNamee shows that striped bass have full stomachs during daylight hours, but that the stomachs gradually empty through the night.
\t\tOne intriguing aspect of Horodysky's research is the disparity he's found between the prey items that striped bass are adapted to see— large, fast-moving fish like menhaden—and the items that actually occur in their stomachs—mostly small crustaceans like juvenile blue crabs and mysid shrimp.
\t\tHorodysky and his faculty advisors hypothesize that striped bass are living in a visual world very different from the one evolution prepared them for. That's because human activities in the Bay watershed and the demise of the native oyster have dramatically reduced the clarity of Bay waters.
\t\t"Chesapeake Bay used to be very clear," says Brill. "Now we've made it mucky. So we see the visual ecology of the Bay changing. Our argument is that over evolutionary time these fish have made certain visual choices, then suddenly find themselves in a visual environment they didn't evolve in."
\t\tThis visual mismatch could have important implications for fisheries managers, who traditionally make management decisions based on the relative abundance of predator and prey—the number of striped bass or menhaden netted per unit area.
\t\t"What we're getting at," says Horodysky, "is that it isn't the number of prey per meter that's most important to these visual predators. It's the number they can see. Is there a visual issue, with the Bay being turbid, being murky? If you can't see very far, how is that affecting your ability to feed? These are larger questions we can begin to chip away at once we get our baseline data. We can't start to answer these questions until we know the limits of the eye."
\t\tIn the meantime, Brill and Horodysky plan to expand their research to other popular recreational fish like \t\tsummer flounder and \t\tcobia, and also to the \t\tforage fish—most notably menhaden—that so many recreational species depend on for food.
\t\tFor Virginia's anglers, the most important question for Horodysky might be how a better understanding of fish vision can give them better luck on the water. "I can't guarantee that anyone who uses these data is going to catch more fish," responds Horodysky. "But they will be able to make more informed choices."
\t\tHorodysky, himself a fly-tier and avid angler, notes that his color research does confirm at least one common saying that Bay anglers use when selecting a lure for striped bass: "If it ain't chartreuse, it ain't no use."
\t\t"Nothing in the wild is ever chartreuse," says Horodysky, "but the color is right smack dab in the middle of a striper's visual range. They can see it really well."
\t\tQuestions or Comments? Contact the News & Media webmaster
post #2 of 11
thats an odd reality,who ever would think that a stripers eyes are built for daylight?

I have found that their eyes are much like a cats having the reflective backing on the retina that allows them to see an image more times and more intensly.

also,I find stripers feeding heavily during non-daylight time.

Chartruese? I would have never fished a plug that color,yellow but not chartruese!
post #3 of 11
chartruse works great onsoft plastics
post #4 of 11

"Nothing in the wild is ever chartreuse," says Horodysky, "but the color is right smack dab in the middle of a striper's visual range. They can see it really well."

can someone explane that to me?
post #5 of 11
This makes sense to me. Perhaps the fishing for stripers (big) is best at night because they are more likely to be fooled by a silhouette and motion (lateral line and obscured vision)?

During the day I frequently see the fish reject flies and lures. Especially big fish. Getting a look isn't that hard.
post #6 of 11
Thread Starter 
Originally Posted by cobia_slayer View Post
can someone explane that to me?

Yeah. It's like putting something in fluorescent orange for us. It makes it stand out so it get noticed from not only the background, but also from further away.
post #7 of 11
MDC, then why do they say "they can't see it real well"

I understand chartreuse is a great color!
post #8 of 11
Thread Starter 
Originally Posted by cobia_slayer View Post
MDC, then why do they say "they can't see it real well"

I understand chartreuse is a great color!

From the article

says Horodysky, "but the color is right smack dab in the middle of a striper's visual range. They can see it really well."
\t\tQuestions or Comments? Contact the News & Media webmaster

The article suggests that in fact they can see it very well. And that makes sense given the graph in the article

The other thing I noticed is that this sorta research was funded by the license fees. Very cool huh?
post #9 of 11
shows why schoolbus and chicken scratch are most popular bomber colors. Bunker colors fall in that green/yellow area too. I know what color my daytime teasers are going to be this spring.
post #10 of 11
I'd be interested to see if they have data on other andromodous and freshwater fish. If I remember correctly, the spectrum of vision of trout and salmon isn't very different from stripers. The other fish mentioned in the study evolved in salt water. If their ancestors had evolved at depths where red doesn't penetrate, diminished sensitivity to red and increased sensitivity to blue and low light levels would be an advantage. There's an extensive literature in that area.

Anyway, "traditional" chartreuse which leans toward yellow, has been a favorite color for striper flies for many decades, and is similar to the yellow lures that catch but don't resemble a yellow fish.
post #11 of 11
This is interesting... On a freshwater scale, when I fish for Largemouths my go-to colors are black and pumpkin. When nothing is hitting I'll throw on the brightest "hows your day glowing" chartreuse and almost always get a response...
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