Panfish, especially crappies and bluegills, tend to be sight feeders, which means they prefer to see it before they eat it. But what’s to see under 3 feet of ice and 2 feet of snow?
Light is diffuse under hard water. Scattered by ice and snow cover, light penetrates but seems to come from all directions. It’s a world without shadow, but hardly a world without light. During the day, it’s not as dark down there as logic might suggest. In fact, it can be quite bright. Even at night, panfish can sight feed under the ice in slightly cloudy to clear water, but probably require a little more help from their lateral line (which picks up vibration) in the dark.
Many studies have been done on the visual acuity of panfish. The ability to see and feed on individual zooplankters has stimulated lots of scientific attention. The eyes of fish are similar to our eyes, with the same basic construction of cornea, iris, lens, and retina. Like us, panfish have multiple cones in the retina that allow for color differentiation. Laboratory tests with bluegills, sunfish, and the closely related black basses seem to indicate that these fish can distinguish one color from another.
So, panfish have the same eyes we do. But different. It’s different underwater. Fish vision expert Dr. Don Quick has likened the optical landscape of fish to walking into a thick, midday fog, where even close objects are obscured by the light reflecting off millions of droplets of water in front of our eyes. The shape of the eye of any fish is specialized, to some degree. In the case of panfish, large, flat, bowl-shaped eyes allow more light in, and focus well on the tiny things panfish need to forage on to survive the first year. But no type of eye construction can see a long distance in fog.
The length of the visual field of panfish depends on water clarity. The maximum distance a fish can see underwater tends to test out about the same as a Secchi-disc reading, which is the distance at which a black-white Secchi disc disappears underwater under bright conditions. This is similar to the distance it takes for a big white jig to disappear under the hole. If your big, bright jig disappears about 10 feet down, it’s safe to assume that the visual field of panfish is limited to slightly more than 10 feet.
BLUEGILLS AND SUNFISH
When bluegills see something that might be food, they reorient themselves and basically go on point, directing the long axis of their bodies in a line with the item that caught their attention. Fisheries biologists and researchers use this reorientation process to determine “reaction distance.” Studies on reaction distance provide some idea about how close a jig has to be from a bluegill to elicit a strike.
A study carried out by William Walton (University of California), Jamie Emiley (Yale), and Nelson Hairston, Jr. (Cornell) focused on the effect of prey size in determining reaction distances in bluegills. They began by sorting daphnia, a species of zooplankton, into three size ranges, from .03 mm up to 2.3 mm in length. Each size group was stored in a separate tissue-culture well and introduced to a tank holding bluegills one at a time by a pipette placed at the opposite end of the tank from the fish. The tank was wrapped in white paper to reduce outside distractions.
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