The term “maximum location distance” (MLD) was used to indicate the outer boundaries of reaction distance. Results included the affirmation that bluegills moved farthest for the biggest prey, again indicating the importance of vision in their foraging strategy. The farthest any bluegill reacted to the largest daphnia was about 46 cm (approximately 17 inches). Considering the size of the prey involved -- smaller than 1/32 of an inch -- that's a remarkable distance. (Extrapolating that to a 3/4-inch jig-maggot combo, reaction distance would be about 34 feet.)
Of course, the water was clear in the aquaria used in this study. The cloudier the water, the shorter a bluegill's range of reaction distance becomes, also indicating the importance of vision in their hunting strategy. In a study on turbidity and bluegill foraging activity carried out by Jeffrey Miner and Roy Stein of the Ohio Fish and Wildlife Research Unit, research found that as light levels increased in turbid water, bluegills foraged on increasingly small items. Also, feeding slowed as turbidity increased. But, no matter how turbid the water, bluegills were able to forage successfully at the highest light levels. In other words, affirming what we already knew, that panfish in turbid water feed best during the middle of the day, regardless of time of year.
William Walton of the University of Maryland reports that the visual resolution of sunfish improves with increasing body size. As sunfish grew from 10 to 38 mm, their MLD increased more than fivefold, due to physiological changes in the eye including the distance between cones in the retina and the location of the pupil relative to the lens center. Apparently, bluegills and sunfish begin their lives nearsighted -- able to focus on tiny objects up close. As they grow, they become increasingly farsighted, better able to react to larger items farther away. This is good news for fishermen.
CRAPPIE VISION
When it comes to ratios between eye size and body size, crappies are king. They have some of the biggest eyes per inch of body length in the freshwater world. This suggests how important vision is to both black and white crappies. In the world of fish, intense predation stress tends to shape animals to fit their environment. Crappies use this adaptive advantage to feed successfully at night. Their large eyes gather more available light than the tiny eyes of baitfish during the dark hours, giving crappies a distinct advantage at night.
This is helpful when describing the sensory world of the crappie -- including any discussion of vision. Little research has been done on the sensory systems of crappies. Since crappies are closely related to sunfish and bass, much of what we suspect about crappie vision has been assimilated from studies of those other species.
Crappies like to inspect things closely. That fact should temper lure selection on ice. Crappies close in for a better look, and unless involved in some kind of competitive feeding spree, they tend to pause and stare before attacking. A live minnow or a small jig-maggot combo are the most likely items to be taken right away by crappies. Plastic baits must have the right size and profile. But all presentations have to be just right, or crappies tend to reject them.
The forward and upward position of the eyes on a crappie indicate that crappies see best and strike most accurately when positioned slightly below their targets. Crappies orient themselves to prospective forage much as bluegills do, turning and aligning themselves with the target, and approaching it until it's just above their snout. As crappies approach a target, they focus their eyes with specialized muscles that move the lens of the eye back and forth as needed. The lens is retracted for scanning a distant object and extended to ogle things close up, like a zoom lens on a camera. This is another adaptive advantage when trying to accurately feed on items as small as daphnia.
