Growth is the ultimate response of an organism to its environment. The objective of this study was to compare growth of lake whitefish ( Coregonus clupeaformis) in Lake Erie and Lake Ontario, from 1954 to 2003. Trends in lake whitefish abundance were similar in Lake Erie and Lake Ontario from the 1950s until 1990, when abundance began to decline in Lake Ontario while remaining relatively stable in Lake Erie. Although both lakes have undergone similar environmental changes, from decreasing phosphorous loading to invasion by dreissenid mussels, declining growth and condition were more pronounced in Lake Ontario. Trends in abundance, growth, and condition of lake whitefish from Lake Erie and Lake Ontario were compared for the period 1990 to 2003. In 2003, lake whitefish were collected from both lakes to describe seasonal diet, energy density, and female GSI. Growth, described as length-at-age, declined significantly in Lake Ontario but did not change in Lake Erie. Lake whitefish energy density (J/g wet mass) was significantly higher in Lake Erie than in Lake Ontario. Biological attributes of lake whitefish from Lake Erie did not change greatly from 1990 to 2003 while fish from Lake Ontario exhibited signs of stress, including decreased size-at-age and condition. (Abstract shortened by UMI.) Source: Masters Abstracts International, Volume: 44-03, page: 1280. Thesis (M.Sc.)--University of Windsor (Canada), 2005.