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Biologists have advanced two theories to explain why schooling of fish occurs in so many fish species. Because schooling is particularly wide spread among species of small fish, both theories assume that schooling offers the advantage of some protection from predators.
Proponents of theory A dispute the assumption that a school of thousands of fish is highly visible. Experiments have shown that any fish can be seen, even in very clear water, only within a sphere of 200 meters in diameter. When fish are in a compact group, the sphere of visibility overlap. Thus, the chance of a predator finding the school is only slightly greater than the chance of the predator finding a single fish swimming alone. Schooling is advantageous to the individual fish because a predator’s chance of finding any particular fish swimming in the school is much smaller than its chance of finding at least one of the same group of fish if the fish were dispersed throughout an area.
However, critics of theory A point out that some fish form schools even in areas where predators are abundant and thus little possibility fo excaping detection exists. They argue that the school continues to be of value to its members even after detection. They advocate theory B, the “confusion effect,” which can be explained in two differe...