How deep can perch feed by sight?

The limit is set by light penetration, not by the fish. In clear Great Lakes water, schools sight-graze on flats of 10 m (33 ft) and deeper at midday; in a stained kettle lake, useful light may quit at 3–4 m (10–13 ft). The fish itself inspects food from only about half a meter (a foot or two) away, so what water clarity really controls is which depths carry enough light for that close-range inspection during the day. That is why the same lake fishes deeper on bright days and shallower under heavy overcast.

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