Yellow perch (Division of Public Affairs/U.S. Fish and Wildlife Service) Is a lake an island? Fisheries managers have tended in the past to think so, treating each lake as a closed system. Man may move freshwater fish around, stocking some here and removing others there, but the fish themselves were judged to be mostly sedentary. Now many ichthyologists are expressing second thoughts, and suggest that, for their finny subjects, lakeshores do not a prison make. “Fish Movement Among Lakes: Are Lakes Isolated?” is the title of a recent paper in Northeastern Naturalist (2008; Volume 15, Number 4) by Robert A. Daniels of the New York State Museum and several colleagues. Since 1995, these researchers have studied fish populations in five lakes linked by streams in the Adirondack Mountains. They netted, tagged, and released adult white suckers, brown bullheads, yellow perch, and other species, and also took advantage of data from local stocking programs that released largemouth bass...