What Fish See–And What they Don’t

This issue will continue exploring the sight of fish, and provide some practical suggestions for anglers. Underwater, where visibility is usually limited to dozens of feet under even the clearest conditions, there is little need for long-range vision.
Fish have been described as being nearsighted, and can probably focus on objects much closer to their eyes than humans can. Cast a popping bug near a school of bluegill and one of them will often approach within an inch of the lure to inspect it—something that would leave an angler cross-eyed! Even when a fish first detects an object off to the side, it will usually turn and face it in order to examine it. Why? The likeliest explanation is that this brings the object within the narrow range of a fish’s binocular vision.
Unlike humans, many fish have their eyes set far apart on the sides of the head rather than to the front. This allows a very wide arc of monocular side vision for spotting predators or prey, but provides only a narrow range of overlapping binocular vision to the front. There is a blind spot to the rear, and the range of binocular vision to the front encompasses only about 30-45 degrees. For this reason, some experienced anglers believe a fish is more likely to spot a lure if it is cast to the fish’s side instead of directly in front of it. Once a fish spots something, turning to face it undoubtedly gives the fish a better estimate of the object’s distance. Even though fish will turn to examine objects, their eyes do have limited independent movement within the sockets. Like humans, a fish’s eyes move in unison when looking around.
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A fish has a narrow range of binocular vision to the front, a wide range of monocular vision to both sides, and a narrow blind spot to the back. Read more